Method for identifying, expanding, and removing adult stem cells and cancer stem cells

ABSTRACT

The invention further relates to means suitable for cancer treatment and even more specific for the treatment of cancer by eradicating cancer stem cells.

RELATED APPLICATIONS

This present invention is a continuation patent application that claims priority to PCT patent application number PCT/NL2008/050543, filed on Aug. 8, 2008, and European application No. 07114192.3, filed on Aug. 10, 2007, the entirety of which are herein incorporated by reference.

The invention relates to the fields of biochemistry, pharmacy and oncology. The invention particularly relates to the use of novel stem cell markers for the isolation of stem cells. The invention further relates to the obtained stem cells and their use in for example research or treatment, for example, for the preparation of a medicament for the treatment of damaged or diseased tissue. The invention further relates to means suitable for cancer treatment and even more specific for the treatment of cancer stem cells.

Adult Stem Cells (Reviewed in 1)

Adult stem cells are found in many, if not all, organs of adult humans and mice. Although there may be great variation in the exact characteristics of adult stem cells in individual tissues, adult stem cells share the following characteristics: They retain an undifferentiated phenotype; their offspring can differentiate towards all lineages present in the pertinent tissue; they retain self-maintenance capabilities throughout life; and they are able to regenerate the pertinent tissue after injury. Stem cells reside in a specialized location, the stem cell niche. The niche typically supplies the appropriate cell-cell contacts and signals to maintain “stemness”.

Some tissues display a high level of steady-state turnover. Good examples are the hematopoietic system, the skin, and the intestinal epithelium. It is assumed that stem cells in such tissues continuously contribute to the self-renewal process. Other tissues, such as the brain, the myocardium or the skeletal muscle, show very little if any proliferative activity in steady-state situations. Stem cells in such tissues are most likely dormant and only become active when differentiated cells are lost, for instance upon injury.

Bone marrow stem cells have been the subject of intensive research over the last 30 years. Work on other adult stem cells has typically been initiated more recently. Good progress has been made with a limited number of these, i.e. the epidermal stem cell, the hair follicle stem cell, neuronal stem cells, and the mammary gland stem cell. In a dramatic demonstration, a single mammary gland stem cell was shown to regenerate the entire mammary epithelium upon introduction into the mammary fat pad (2).

The study of stem cells has two prerequisites:

1) It has to be possible to recognize and isolate live primary stem cells. The availability of specific (combinations of) markers is essential. As exemplified by the seminal studies in human and mouse bone marrow, combinations of cell surface markers allow the sorting of strongly enriched populations of cells. 2) In vitro cell culture or in vivo transplantation assays subsequently allow the demonstration of long-term generation of all differentiated cell types. Typically, from these assay systems, stem cells are re-isolated and serially assayed to demonstrate long-term stemness and self-renewal.

As a non-limiting example of adult stem cells, intestinal stem cells are discussed in more detail.

Intestinal Stem Cells

The intestinal epithelium is the most rapidly self-renewing tissue in the adult. A handful of stem cells are believed to be located at the base of each intestinal crypt to ensure continuous and unlimited renewal. Compared to the other rapidly self-renewing tissues, the intestinal stem cells have remained rather elusive. No ex vivo or transplantation assays exist for these cells, and all knowledge of intestinal stem cells derives from histological analysis of crypts in situ. Intestinal stem cells divide slower than their proliferating descendants that fill the upward positions of the crypt. While the consensus is that colon stem cells are positioned at the bottom of the crypts, the localization of stem cells in the small intestine remains a controversial issue. Potten and colleagues have provided evidence supporting a localization immediately above the Paneth cell compartment at position +4, using the Long Term DNA label Retention assay (reviewed in 3,4). Lineage tracing studies have instigated Bjerknes and Cheng to propose that a different cell-type, the so called crypt base columnar cell, may represent the genuine stem cell. These crypt base columnar cells are intermingled with Paneth cells at the bottom-most positions of the crypts (5).

Only recently some candidate gene markers for intestinal stem cells have been proposed: i.e. Musashi (6,7) and phospho-PTEN (8). We and others find that the Musashi expression domain contains 30-50 cells per crypt, many more than there are stem cells (see below), while the phospho-PTEN mark may represent an artifact (9).

The number of stem cells in adult crypts has been estimated between 1 and 6 depending on the experimental approach used (10). It remains a matter of debate whether stemness is a set of properties that are self-perpetuated by asymmetric division through the years or whether the crypt bottom acts as a niche that confers these properties to progenitors residing within. The study of cell pedigrees in single crypts by analysis of methylation tags (11) indicates that stem cells divide stochastically in asymmetric (i.e. one daughter stem cell plus one differentiating progenitor) or symmetric fashion (i.e. either two stem cells daughters or two differentiating progenitors). Of note, while the existence of asymmetric and symmetric cell divisions is inferred from the above studies, no formal proof of asymmetric distribution of determinants during mitosis in the intestinal epithelium has been observed so far.

When they reach the top third of colorectal crypts (or the villus in the small intestine), committed progenitors differentiate into absorbtive cells (colonocytes/enterocytes) or secretory lineage cells (goblet cells, enteroendocrine cells, Paneth cells). From this point onwards, differentiated cells continue their migration towards the villus in coherent bands stretching along the crypt-villus axis or organised at the surface epithelium of the colorectum in clusters of hexagonal appearance. As an exception to this rule, Paneth cells migrate towards the crypt bottom in the small intestine (reviewed in 12).

Cancer Stem Cells (Reviewed in 13, 14)

The cancer stem cell hypothesis postulates that a small reservoir of self-sustaining cells is exclusively able to self-renew and maintain the tumor. These cancer stem cells can expand the cancer stem cell pool, but will also generate the heterogeneous cell types that constitute the bulk of the tumor. Cancer stem cells may be relatively refractory to therapies that have been developed to eradicate the rapidly dividing cells that constitute the bulk of a tumor. Cancer stem cells may also be the most likely cells to metastasize. Thus, the cancer stem cell hypothesis would require that we rethink the way we diagnose and treat tumors. Therapy would have to target the “minority” stem cell population that fuels tumor growth and metastasis, rather than the bulk of the tumor. The cancer stem cell hypothesis is at the centre of a rapidly evolving field and may dictate changes in how basic and clinical researchers view cancer.

In the 1990s, studies by John Dick and others on acute myelogenous leukemia (AML) supported the existence of cancer stem cells in this disease (15, 16). Efforts to define the cell of origin in hematopoietic malignancies were greatly helped by the availability of heamatopoietic lineage maps, and of cell surface markers for distinct cell types and lineages. The putative AML stem cells were demonstrated to be capable of regenerating human AML in irradiated NOD/SCID mice. The AML stem cell displayed a CD34⁺CD38⁻ phenotype, similar to that of normal human hematopoietic progenitors, suggesting a close similarity between AML stem cells and normal stem cells.

Recently, cancer stem cells have also been identified in a number of solid tumors. Clarke and colleagues transplanted fractioned cells from human breast tumors into NOD/SCID mice. As few as a hundred CD44⁺CD24⁻/low cells could establish tumors in mice, whereas tens of thousands of cells from different fractions failed to induce tumors (17). This example has been followed by multiple other studies on solid tumors. For instance, brain tumor stem cells that can produce serially transplantable brain tumors in NOD/SCID mice have been isolated from human medulloblastomas and glioblastomas using the CD133 marker found also on normal neural stem cells (reviewed in 18). Sorting for Hoechst dye—excluding side population (SP) cells and for CD44 allowed the isolation of cancer stem cells in prostate cancer (reviewed in 19).

There is some confusion in the literature as to the definition of a cancer stem cell. Here, we follow the consensus reached at a recent AACR workshop (14), which states that the cancer stem cell “is a cell within a tumor that possesses the capacity to self-renew and to cause the heterogeneous lineages of cancer cells that comprise the tumor. Cancer stem cells can thus only be defined experimentally by their ability to recapitulate the generation of a continuously growing tumor”. Alternative terms in the literature include tumor-initiating cell and tumorigenic cell. Assays for cancer stem cell activity need to address the potential of self-renewal and of tumor propagation. The gold-standard assay currently is serial xeno-transplantation into immunodeficient mice.

As a non-limiting example of cancer stem cells, colon cancer stem cells are discussed in more detail.

Colon Cancer Stem Cells

Can the cancer stem cell hypothesis be extrapolated to human colon cancer? Two very recent studies imply that this is the case. John Dick and colleagues explored the usefulness of CD133 as a marker for colorectal cancer cells (20). CD133 or Prominin, is a marker that is associated with stem and progenitor populations in multiple tissues and cancers. They found that CD133 was expressed on 5-20% of human colon cancer cells. Subsequent serial xenograft assays demonstrated that CD133+, but not CD133− cells could initiate tumor formation in immunodeficient mice. It was calculated that the frequency of cancer stem cells in the isolated CD133+ population was slightly less than 0.5%. Along similar lines, De Maria and colleagues found that CD133+ cells comprised less than 2.5% of human colon cancer cells and also demonstrated that these cells could be serially transplanted into immunodeficient mice (21). Moreover, the CD133+ cells could be maintained for long periods of time in culture using a serum-free medium containing EGF and FGF2.

These studies imply that colon cancer may represent another example of a solid tumor in which a small number of cancer stem cells is responsible for maintenance of the tumor. Sorting for expression of the CD133 marker enriches significantly for the cancer stem cell, but the resulting cell mixture remains far from pure. It therefore remains unclear what the exact properties are of the cancer stem cells within the sorted cell preparation, such as their cell cycle status, or their resistance to chemotherapy or radiation.

US 2004/0058392 and EP 1 400 807 describe a list of TCF target genes that were defined in the colon cancer cell line Ls174T (22). In the applications, it was speculated that these molecules expressed in colon cancer cells and in intestinal crypts would represent stem cell markers. Several of the markers encode cell-surface proteins. The inventors of US 2004/0058392 and EP 1 400 807 contemplated that these proteins can be used as markers for selection of the abundant stem cell population in the gut. However, it turned out that the overwhelming majority of these proteins are not suitable as a stem cell selection marker as they are not expressed (specifically) by stem cells. E.g. the CD44 protein is expressed by all dividing crypt cells (23) as is cMyb (24) and GPX2 (25). The c-Kit protein is expressed on non-dividing entero-endocrine cells (26). EphB2 is expressed by all dividing cells and EphB3 is expressed by the non-dividing Paneth cells (27). BMP4 is expressed by stromal cells in the villus (28). And Claudin1 is expressed almost ubiquitously (29).

The present invention provides markers that identify adult and/or tissue stem cells and cancer stem cells. The identified adult and/or tissue stem cells are useful in the repair of damaged or diseased tissue. The present invention further provides methods that allow for the isolation of adult and/or tissue stem cells and/or cancer stem cells. The invention further provides ex vivo methods for culturing or maintaining or multiplying (isolated) adult and/or tissue stem cells and/or cancer stem cells. The invention yet further provides methods that allow the identification and eradication of cancer stem cell markers. One of the objects of the present invention is to provide novel markers that are useful in a method for identifying adult stem cells and cancer stem cells. Another object of the present invention is to provide a method suitable for maintaining/culturing/multiplying/expanding adult stem cells. Yet another object of the present invention is to eradicate cancer stem cells. Adult stem cells are typically isolated from tissue and are therefore also referred to as tissue stem cells.

The surface receptors Lgr5 and Lgr 6 mark adult stem cells in multiple tissues as well as cancer stem cells in multiple types of cancer. The present inventors disclose that the expression patterns of the surface molecules Lgr5 (also known as Grp49) and of Lgr6 independently mark adult stem cells in multiple tissues, as well as cancer stem cells in multiple types of cancer. Glycoprotein hormone receptors, such as the receptors for LH, FSH, and TSH, belong to the large G protein-coupled receptor (GPCR) superfamily, but are unique in carrying a large leucine-rich ectodomain important for ligand binding. These leucine-rich repeat-containing, G protein-coupled receptors in the human genome are termed LGRs. Phylogenetic analysis shows that there are three LGR subgroups: the known glycoprotein hormone receptors; LGR4 to 6; and a third subgroup represented by LGR7 (30). LGR5 and -6 are the main subject of this invention. Ligands for these two receptors remain not described in the scientific literature; hence these receptors are often referred to as orphans. Sequences of the human, mouse and rat receptors are shown in FIG. 10. Human LGR4 comprises 951 amino acids, 447 of which are identical to the corresponding amino acids in LGR5 and 485 of which are identical to the corresponding amino acids in LGR6. Human LGR5 comprises 907 amino acids, 387 of which are identical to the corresponding amino acids in LGR6. LGR6 consists of 967 amino acids. A predicted structure of these receptors is given in FIG. 11. LGR4/GPR48 is the best studied gene of the three. According to the scientific literature, it is broadly expressed in multiple tissues (31, 32) and not associated specifically with stem cells. In genetic mouse models, it has been described to be important for intrauterine growth (32), for male fertility (33) and for renal development (34). LGR5/GPR49 has been knocked out. Mutant embryos die after birth due to a defect in the tongue and lower jaw (35). LGR5/GPR49 is overexpressed in hepatic and colon cancers (22, 36, 37). LGR6 has not been studied beyond its initial cloning and sequence analysis (30).

In a first embodiment, the invention provides a method for obtaining (or isolating) adult stem cells comprising

-   -   optionally preparing a cell suspension from a normal tissue or         organ sample     -   contacting said cell suspension with an Lgr5 and/or 6 binding         compound     -   identify the cells bound to said binding compound     -   optionally isolating the stem cells from said binding compound.

A method of the invention allows obtaining (or isolating) a collection of cells comprising, preferably consisting of, at least 50%, more preferred at least 60%, more preferred at least 70%, more preferred at least 80%, most preferred at least 90% stem cells, such as between 90% and 99% stem cells or between 95% and 99% stem cells, the method comprising

-   -   optionally preparing a cell suspension from a normal tissue or         organ sample     -   contacting said cell suspension with an Lgr6 and/or 5 binding         compound     -   identify or obtaining cells bound to said binding compound     -   optionally isolating the stem cells from said binding compound.

The isolated collection of stem cells comprises, and preferably consists of, more than 50%, more preferred at least 60%, more preferred at least 70%, more preferred at least 80%, most preferred at least 90% stem cells, such as between 90% and 99% stem cells or between 95% and 99% pure pluripotent stem cells, which can retain an undifferentiated phenotype. The cells retain self-maintenance capabilities throughout life; and are able to regenerate the pertinent tissue after injury. Their offspring, or non-stem cell daughter cells, can differentiate towards all lineages present in the pertinent tissue. Said collection of cells can be isolated from a cell suspension comprising stem cells and non-stem cell daughter cells such as committed or differentiated daughter progenitor cells. An adult stem cell is preferably a stem cell obtained from a post embryonic tissue. Preferably a post natal tissue. In primates such as a human they are preferably obtained from at least a year old subject, preferably a post-puberal subject. In a preferred embodiment of the invention said stem cells are adult stem cells and/or cancer stem cells.

A major advantage of a collection of stem cells comprising more than 50% pluripotent stem cells is that said population comprises less cells that can act negatively on the self maintenance capacity of the stem cells and/or the differentiation capacity of the stem cells, compared to a collection of stem cells comprising less than 50% pure pluripotent stem cells. These negatively acting cells comprise non-stem cell daughter cells or other non-stem cells that are co-isolated with the stem cells.

Further advantages of a pure, or almost pure, population of adult stem cells are that limited cell numbers can be used as therapeutic agent for the treatment of diseases in which the corresponding tissue has been affected, of which the composition is well known.

Preferably, said stem cells are tissue stem cells, such as for instance intestinal stem cells, skin stem cells or retina stem cells. The invention preferably provides a method for isolating tissue stem cells, said method comprising the above described steps. Said stem cells do not include human embryonic stem cells. When isolating adult and/or tissue stem cells it is preferred to start with a collection of cells from the specific tissue from which the tissue and/or adult stem cell is to be isolated. Typically a tissue stem cell and/or adult stem cell is committed to form cells of said tissue, however, a tissue and/or adult stem cell can exceptionally be manipulated to produce cells of another tissue.

Stem cells are primal cells found in all multi-cellular organisms. They retain the ability to renew themselves through mitotic cell division and can differentiate into a diverse range of specialized cell types. The three broad categories of mammalian stem cells are: embryonic cells (derived from blastocysts), adult stem cells (which are found in adult tissues) and cord blood stem cells (which are found in the umbilical cord). The definition of a stem cell requires that it is at least capable of self-renewal (the ability to go through numerous cycles of cell division while maintaining the undifferentiated state) and has an unlimited potency (the capacity to differentiate into any mature cell type, i.e. being either totipotent, pluripotent, multipotent or unipotent).

In a preferred embodiment, the invention provides a method for obtaining (or isolating) stem cells comprising

-   -   optionally preparing a cell suspension from a normal tissue         sample     -   contacting said cell suspension with an Lgr 5 and/or 6 binding         compound     -   identify or obtaining the cells bound to said binding compound     -   optionally isolating the stem cells from said binding compound,         wherein said stem cells are adult stem cells, more preferably         mammalian adult stem cells and even more preferably human adult         stem cells. These adult stem cells typically act as a repair         system for the body and are replenishing specialized cells.         Adult stem cells are found in children as well as in adults and         most adult stem cells are lineage restricted (multipotent) and         are referred to by their tissue origin, for example skin stem         cell or retina stem cell.

A tissue or organ sample can be obtained via any known method, such as a biopsy. Moreover, a tissue or organ sample can be obtained from any possible tissue or organ, such as, but not limited to, heart, retina, breast, ovary, lung, brain, eye, stomach, pancreas, liver, intestine comprising colon and rectal tissue, skin, hair follicle, and adrenal medulla,

The phrase “a normal tissue or organ sample” is used herein to refer to a tissue or organ sample which is healthy, non-transformed, non-malignant, non-cancerous or non-tumorigenic, i.e. a healthy, non-transformed, non-malignant, non-cancerous or non-tumorigenic tissue or organ sample. Any pathologist, skilled in the art, can determine if a tissue is healthy non-transformed, non-malignant, non-cancerous, or non-tumorigenic.

In a preferred embodiment, the used tissue or organ sample is of mammalian human origin. Even more preferably, the tissue is adult tissue (i.e. tissue of a borne mammal, i.e. non-embryonic/fetal tissue).

Bone marrow and (cord) blood can be considered natural cell suspensions. From solid organs, cell suspensions can be obtained for instance by mechanical disruption of organ tissue into small fragments. These fragments can then optionally be further segregated into single cells by chemicals such as EDTA and/or by enzymatic digestion with for instance the enzyme preparations trypsine, dispase, collagenase or pancreatin. The procedure can involve tissue or cell culture before, during or after the disruption and/or enzymatic digestion procedures

As it is not always necessary to isolate the stem cells from the used binding compound, said step is presented as an optional feature in the claim. When it is necessary to isolate the stem cells from the Lgr 5 and/or 6 binding compound, this can be performed by multiple methods well known to the skilled person. Suitable examples are (mechanical) agitation, enzymatic digestion, addition of excess binding compound or a derivative thereof, elution by changing pH or salt concentration.

Now that the inventors have provided evidence that Lgr5 or 6 are (unique) markers for stem cells, compounds that are capable of binding to Lgr5 and/or 6 (i.e. Lgr5 or 6 binding compounds) can be used to identify, mark and isolate stem cells.

One suitable example of an Lgr5 or 6 binding compound is an antibody or an antibody derivative or an antibody fragment capable of binding to Lgr5 or 6, i.e. an antibody or derivative or fragment thereof that has affinity for Lgr5 or 6. As Lgr5 and 6 are transmembrane surface proteins, such an antibody or a derivative or a fragment thereof preferably has affinity for the part of the protein facing externally, i.e. binds to any extracellular part. In a preferred embodiment, said antibody or an antibody derivative or an antibody fragment has a high affinity for Lgr5 and/or 6.

Hence, in a preferred embodiment, the invention provides a method for obtaining (or isolating) stem cells comprising

-   -   optionally preparing a cell suspension from a normal tissue or         organ sample     -   contacting said cell suspension with an Lgr5 and/or 6 binding         compound     -   identify or obtaining the cells bound to said binding compound     -   optionally isolating the stem cells from said binding compound,         wherein said Lgr5 and/or 6 binding compound is an antibody or an         antibody derivative or an antibody fragment capable of binding         to Lgr5 and/or 6.

Antibodies or their derivatives and/or their fragments can be provided by methods that are well known to the person skilled in the art and include the hybridoma technology in normal or transgenic mice or in rabbits, or phage display antibody technology. In one embodiment, genetic immunization is used. This technique comprises administration of a nucleic acid sequence, or a functional equivalent thereof, encoding at least one antigen of interest, to a non-human animal. The encoded antigen(s) is/are produced by the animal, which stimulates the animal's immune system against said antigen(s). Hence, an immune response against said antigen(s) is elicited in said animal. Subsequently, T-cells, B-cells and/or antibodies specific for an antigen of interest are preferably obtained from said animal. Said T-cells, B-cells and/or antibodies are optionally further processed. In one preferred embodiment, an obtained B-cell of interest is used in hybridoma technology wherein said obtained B-cell is fused with a tumor cell in order to produce a hybrid antibody producing cell.

Examples of suitable antibody fragments are scFv, Fab, or (Fab)2 fragments. Examples of suitable derivatives are chimeric antibodies, nanobodies, bifunctional antibodies or humanized antibodies.

In yet another preferred embodiment, the used antibody is a monoclonal antibody.

In a further preferred embodiment, a Lgr5 and/or 6 binding compound comprises an antibody or an antibody derivative or an antibody fragment comprising a heavy chain CDR1, CDR2 and/or CDR3 sequence as depicted in FIG. 27, and preferably also comprising a complementary immunoglobulin light chain molecule, whereby the CDR sequences are determined according to Kabat (Kabat et al., “Sequences of Proteins of Immunological Interest,” U.S. Dept. of Health and Human Services, National Institute of Health, 1987). Preferably, said antibody or antibody derivative or antibody fragment comprises the heavy chain CDR1 sequence and the heavy chain CDR2 sequence and the heavy chain CDR3 sequence of a heavy chain as depicted in FIG. 27. It was found by the inventors that an antibody or an antibody derivative or an antibody fragment, such as for example a scFv, Fab, or (Fab)2 fragment, comprising a heavy chain CDR1, CDR2 and/or CDR3 sequence as depicted in FIG. 27 constitutes a high affinity binding compound with a high specificity for their target proteins.

In a further preferred embodiment, a Lgr5 and/or 6 binding compound comprises an antibody or an antibody derivative or an antibody fragment comprising a light chain CDR1, CDR2 and/or CDR3 sequence as depicted in FIG. 27, and preferably also comprising a complementary immunoglobulin heavy chain molecule, whereby the CDR sequences are determined according to Kabat (Kabat et al., “Sequences of Proteins of Immunological Interest,” U.S. Dept. of Health and Human Services, National Institute of Health, 1987). Preferably, said antibody or antibody derivative or antibody fragment comprises the light chain CDR1 sequence and the light chain CDR2 sequence and the light chain CDR3 sequence of the light chain as depicted in FIG. 27. It was found by the inventors that an antibody or an antibody derivative or an antibody fragment, such as for example a scFv, Fab, or (Fab)2 fragment, comprising a light chain CDR1, CDR2 and/or CDR3 sequence as depicted in FIG. 27 constitutes a high affinity binding compound with a high specificity for their target proteins.

In one preferred embodiment, a Lgr5 and/or 6 binding compound comprises an antibody as depicted in Table 4 or 5.

A method according to the invention, wherein an antibody as depicted in Table 4 or 5 is used is therefore also herewith provided, as well as a method according to the invention, wherein an antibody or an antibody derivative or an antibody fragment is used which comprises at least one CDR sequence as depicted in FIG. 27. Preferably, said antibody or antibody derivative or antibody fragment comprises a CDR1 sequence and a CDR2 sequence and a CDR3 sequence of a light chain and/or heavy chain depicted in FIG. 27.

In a specific embodiment, a binding compound comprising a heavy chain and/or a light chain CDR1, CDR2 and/or CDR3 sequence as depicted in FIG. 27, is a rat monoclonal antibody. In preferred embodiment, a binding compound comprising a heavy chain and/or a light chain CDR1, CDR2 and/or CDR3 sequence as depicted in FIG. 27, is a chimaeric, deimmunized, or humanized monoclonal antibody. Methods for generating a chimaeric, deimmunized, or humanized monoclonal antibody or derivative or fragment thereof comprising a heavy chain and/or a light chain CDR1, CDR2 and/or CDR3 sequence as depicted in FIG. 27, are known in the art. For example, a chimaeric antibody can be generated comprising a rodent variable region comprising the indicated CDR sequence(s) fused to a non-rodent, for example a human, constant region (Morrison et al. 1984. Proc Natl Acad Sci USA 81: 6851-6855; which is hereby incorporated by reference). Methods for deimmunization of a binding compound comprising a heavy chain and/or a light chain CDR1, CDR2 and/or CDR3 sequence as depicted in FIG. 27 are also known to a skilled person, for example from Giovannoni, 2003. Neurology 61: S13-S17; which is hereby incorporated by reference. Humanization of a non-human antibody is principally achieved through grafting of the CDR regions to a human immunoglobulin framework region as is shown, for example, in U.S. Pat. No. 6,548,640, U.S. Pat. No. 5,530,101, and U.S. Pat. No. 5,859,205, which are all hereby incorporated by reference.

A human antibody against Lgr5 or 6 can also be generated in an animal provided with human sequences encoding an immunoglobulin heavy and/or light chain gene such as transgenic strains of mice in which mouse antibody gene expression is suppressed and effectively replaced with human antibody gene expression. Examples are provided by the HuMAb®-Mouse technology of Medarex; the TC Mouse™ technology of Kirin, and the KVM-Mouse® technology, a crossbred mouse that combines the characteristics of the HuMAb-Mouse with the TC Mouse.

The invention further provides the use of a binding compound according to the invention for identifying or isolating stem cells from a population of cells comprising stem cells and committed or differentiated daughter progenitor cells; whereby the isolated stem cells comprise at least 50% pure pluripotent stem cells.

Another example of an Lgr5 or 6 binding compound is an Lgr5 or 6 ligand. Such an Lgr5 or 6 ligand can be used unmodified, can be produced and/or used as a fusion protein (i.e. a ligand fusion protein) or can be coupled to a second moiety to, for example, allow cell separation.

In a preferred embodiment, the invention therefore provides a method for obtaining (or isolating) stem cells comprising

-   -   optionally preparing a cell suspension from a normal tissue or         organ sample     -   contacting said cell suspension with an Lgr5 and/or 6 binding         compound     -   identify or obtaining the cells bound to said binding compound     -   optionally isolating the stem cells from said binding compound,         wherein said Lgr5 and/or 6 binding compound is a Lgr5 or 6         ligand, for example a ligand fusion protein.

The person skilled in the art is very well capable of producing an Lgr5 or 6 ligand fusion protein, for example via standard molecular biology techniques.

A suitable example of an Lgr5 or 6 ligand is a member of the insulin peptide family, such as Insl5 or relaxin3. Another suitable example is a cysteine-knot protein such as Noggin, Gremlin1 or -2, Dan, or Cerberus. The nucleotide and amino acid sequences of these ligands are known and the skilled person is thus for example capable to produce a ligand fusion protein.

Preferably the second moiety of a ligand fusion protein introduces a feature which allows for easy identification and tracing of the fusion protein, for example a protein (fragment) such as the antibody Fc tail or Staphylococcal protein A or Glutathion-S-transferase, a short antigenic peptide tag such as the Myc, FLAG or HA tag or an oligomeric Histidine-tag, an enzymatic tag such as Alkaline Phosphatase, a fluorescent protein tag such as Green Fluorescent Protein. Small chemical moieties can also be coupled to the ligand for stem cell identification and/or isolation. These moieties can be recognized and bound by specific antibodies, or can have specific affinity for a material to be used in cell separation, or can for instance be fluorescent. In an even more preferred embodiment, the second part of the fusion protein is linked to an Lgr5 or 6 ligand via a spacer. Even more preferable, said spacer comprises an enzyme digestible sequence. This allows for an easy separation of the second moiety and the Lgr5 or 6 ligand.

Yet another example of an Lgr5 or 6 binding compound is a small compound that has affinity for Lgr5 or 6.

In a preferred embodiment, the invention thus provide a method for obtaining (or isolating) stem cells comprising

-   -   optionally preparing a cell suspension from a normal tissue or         organ sample     -   contacting said cell suspension with an Lgr5 and/or 6 binding         compound     -   identify or obtaining the cells bound to said binding compound     -   optionally isolating the stem cells from said binding compound,         wherein said Lgr5 or 6 binding compound is a small molecule with         affinity for Lgr5 or 6. A suitable example is a small chemical         molecule or a small non-chemical molecule or a small protein.

In a preferred embodiment, the affinity of said small molecule for Lgr5 or 6 is a high affinity, i.e. an affinity with a Kd of at least 10⁻⁷.

As already outlined above, the invention provides a method for obtaining (or isolating) stem cells comprising

-   -   optionally preparing a cell suspension from a normal tissue or         organ sample     -   contacting said cell suspension with an Lgr5 and/or 6 binding         compound     -   identify or obtaining the cells bound to said binding compound     -   optionally isolating the stem cells from said binding compound,         wherein said cells are preferably (adult) (tissue) stem cells.

Non-limiting examples of stem cells that can be obtained via the above mentioned methods are skin, intestinal comprising colon and rectal, eye, retina, brain, breast, hair follicle, pancreas, stomach, liver, lung, heart, adrenal medulla, or ovarian stem cells. It has not been previously been possible to obtain or isolate stomach, intestinal or retina stem cells. Hence, in a preferred embodiment, the obtained or isolated stem cells are stomach, intestinal or retina stem cells.

Depending on the desired adult and/or tissue stem cell and the presence or absence of Lgr5 and/or 6, a method according to the invention can be performed with at least one, at least two, at least three or even more (different) binding compound(s). Table 1 provides an overview of the presence or absence of Lgr5 or 6 on different kind of adult and/or tissue stem cells. Based on Table 1 the person skilled in the art is very well capable of selecting one or multiple target markers and one or multiple corresponding binding compounds and to obtain or isolate stem cells from a particular normal tissue or organ.

TABLE 1 The distribution of the adult and/or tissue stem cell markers Lgr5 and 6 marker stem cell Lgr5 Lgr6 brain + + kidney − − liver + − lung − + retina + − stomach + − intestine + − pancreas + − testis − − breast + + hair follicle + + heart − + ovary + − adrenal medulla + − skin + + bladder + − bone + − connective tissue + + ear + − muscle + − prostate + − placenta + − uterus + + bone marrow − + eye − +

If the person skilled in the art wants, for example, to obtain breast stem cells, a binding compound of Lgr5 or 6 can be used alone or in any combination thereof, because the breast stem cells comprise both of said markers.

In a preferred embodiment, the invention provides a method for obtaining (or isolating) stem cells comprising

-   -   optionally preparing a cell suspension from a normal tissue or         organ sample     -   contacting said cell suspension with an Lgr5 and/or 6 binding         compound     -   identify or obtaining the cells bound to said binding compound     -   optionally isolating the stem cells from said binding compound,         wherein     -   said Lgr5 and/or 6 binding compound is an Lgr5 binding compound         and wherein said stem cells are brain, liver, retina, stomach,         intestine, pancreas, ovary, hair follicle, adrenal medulla,         skin, bladder, bone, ear, muscle, prostate, placenta, or breast         stem cells; or     -   said Lgr5 and/or 6 binding compound is an Lgr6 binding compound         and wherein said stem cells are brain, skin, lung, breast, hair         follicle, bone marrow, eye, or heart stem cells; or     -   said Lgr5 and/or 6 binding compound is at least one Lgr6 binding         compound in combination with at least one Lgr5 binding compound         and wherein said stem cells are brain, breast, skin, connective         tissue, uterus, or hair follicle stem cells.

In yet another preferred embodiment, the invention provides a method for obtaining (or isolating) stem cells comprising

-   -   optionally preparing a cell suspension from a normal tissue or         organ sample     -   contacting said cell suspension with an Lgr5 and/or 6 binding         compound     -   identify or obtaining the cells bound to said binding compound     -   optionally isolating the stem cells from said binding compound,         wherein said stem cell is any of the stem cells identified in         Table 1 and wherein the used Lgr5 and/or 6 binding compound         corresponds to the desired stem cell as shown in Table 1, with         the proviso that in case the stem cell is an intestinal or hair         follicle cell, the Lgr5 or 6 binding compound is not uniquely         targeting Lgr5 (i.e. is not a Lgr5 binding compound alone).

In a preferred embodiment, the invention provides a method for obtaining (or isolating) stem cells comprising

-   -   optionally preparing a cell suspension from a normal tissue or         organ sample     -   contacting said cell suspension with an Lgr5 and/or 6 binding         compound     -   identify or obtaining the cells bound to said binding compound     -   optionally isolating the stem cells from said binding compound,         wherein one binding compound is used.

In yet another preferred embodiment, the invention provides a method for obtaining (or isolating) stem cells comprising

-   -   optionally preparing a cell suspension from a normal tissue or         organ sample     -   contacting said cell suspension with an Lgr5 and/or 6 binding         compound     -   identify or obtaining the cells bound to said binding compound     -   optionally isolating the stem cells from said binding compound,         wherein at least two different binding compounds are contacted         with said cell suspension. Said two different binding compounds         can be directed against one and the same marker (i.e. directed         to Lgr5 or to Lgr6). For example use can be made of two         antibodies directed to two different epitopes which antibodies         together provide (a preferably essentially complete) capture of         the desired stem cells. However, said two different binding         compounds can also be directed to two different stem cell         markers (i.e. one binding compound for Lgr5 and one for Lgr6).         Whenever use is made of two or three or even more binding         compounds, said binding compounds may be from the same class of         binding compounds (for example all being antibodies, small         molecules or ligand fusion proteins) or may be from different         classes of binding compounds (for example an antibody directed         to Lgr6 and a ligand fusion protein for binding to Lgr5).

In a preferred embodiment, at least two different antibodies or antibody derivatives or antibody fragments capable of binding to Lgr5 or 6 are contacted with a cell suspension.

After allowing the binding compounds to interact with the cell suspension (for a certain amount of time or under different conditions such as pH, temperature, salt etc.), subsequent identification of obtained bound complexes is performed. This is for example accomplished by using FACS analysis. Fluorescence-activated cell-sorting (FACS) is a specialised type of flow cytometry. It provides a method for sorting a heterogeneous mixture of biological cells into two or more containers, one cell at a time, based upon the specific light scattering and fluorescent characteristics of each cell. It is a useful scientific instrument as it provides fast, objective and quantitative recording of fluorescent signals from individual cells as well as physical separation of cells of particular interest.

In a preferred embodiment, the invention provides a method for obtaining (or isolating) stem cells comprising

-   -   optionally preparing a cell suspension from a normal tissue or         organ sample     -   contacting said cell suspension with an Lgr5 and/or 6 binding         compound     -   identify or obtaining the cells bound to said binding compound     -   optionally isolating the stem cells from said binding compound,         wherein a FACS is used to identify and sort the cells that bind         to an Lgr5 or 6 binding compound.

Other options for isolation of stem cells utilizes binding compounds bound to Lgr5 or 6 on stem cells in conjunction with magnetic bead sorting, immunoaffinity column cell separation or panning.

For analysis by FACS, the binding compound is provided with a fluorescence label, for analysis by magnetic bead sorting the binding compound is provide with magnetic beads (for example an antibody-coated magnetic bead), for immunoaffinity it is bound to a solid support, for panning to tissue culture dishes.

Now that we know that Lgr5 and/or 6 are markers for adult stem cells, this knowledge can also be used in respect of the culturing of adult stem cells. Ligands of Lgr5 and/or 6 as well as small molecule agonists of Lgr5 and/or 6 can be used as a stimulator for the growth of normal (i.e. healthy, non-transformed, normal) adult stem cells.

The invention therefore also provides a method for maintaining or culturing tissue or organ stem cells, comprising providing tissue or organ stem cells with an Lgr5 and/or 6 ligand or a small molecule agonist of Lgr5 and/or 6.

The term “maintaining” is used herein to describe the situation in which the number of stem cells is essentially not changed. The term “culturing” is used herein to describe the situation in which the amount of stem cells is increased, i.e. in which the cells are expanded while retaining their stem cell phenotype.

After the tissue or organ stem cells have been provided with an Lgr5 and/or 6 ligand, the cells are incubated in tissue culture at circumstances (temperature, culture medium, pH) that allow for maintenance or expansion.

The stem cells can be obtained via any suitable method but are preferably obtained by any of the methods described herein, i.e. a method for obtaining (or isolating) stem cells comprising

-   -   optionally preparing a cell suspension from a normal tissue or         organ sample     -   contacting said cell suspension with an Lgr5 and/or 6 binding         compound     -   identify or obtaining the cells bound to said binding compound     -   optionally isolating the stem cells from said binding compound.

In a preferred embodiment, the invention provides a method for maintaining or culturing tissue or organ stem cells, comprising providing tissue stem cells with an Lgr5 and/or 6 ligand or a small molecule agonist of Lgr5 and/or 6, wherein said ligand is a member of the insulin peptide family. A suitable example of an Lgr5 or 6 ligand is a member of the insulin peptide family, such as Insl5 or relaxin3. Another suitable example is a cysteine-knot protein such as Noggin, Gremlin 1 or 2, Dan, or Cerberus.

The invention further provides (isolated) stem cells, or a collection of isolated stem cells, preferably from mammalian origin and even more preferably human stem cells or human adult stem cells, wherein at least 50% of the cells are Lgr5 or 6 positive, pluripotent stem cells. Preferably, at least 60% of the cells are Lgr5 or 6 positive, pluripotent stem cells. More preferably, at least 70% of the cells are Lgr5 or 6 positive, pluripotent stem cells. More preferably, at least 80% of the cells are Lgr5 or 6 positive, pluripotent stem cells. More preferably, at least 90% of the cells are Lgr5 or 6 positive, pluripotent stem cells. Most preferably, at least 95% of the cells are Lgr5 or 6 positive, pluripotent stem cells. The purity of the collection can be increased as indicated herein above. In a preferred embodiment the invention provides (isolated) stem cells or a collection of isolated stem cells wherein said stem cells contain bound specific Lgr5 and/or Lgr6 binding compound. Preferably a specific Lgr5 and/or Lgr6 binding antibody as described herein above or a fragment or derivative thereof. The invention further provides a culture of stem cells comprising a binding antibody specific for Lgr5 and/or Lgr6 or a specific fragment of at least 20 amino acids of said Lgr5 and/or Lgr6 binding antibody.

In a preferred embodiment, said stem cells are, or said collection of stem cells comprises, brain, liver, retina, stomach, intestine including colon and rectal, ovary, hair follicle, adrenal medulla, skin, bladder, bone, connective tissue, ear, muscle, prostate, placenta, uterus, or breast stem cells that comprise Lgr5 in their cell membrane.

In a particularly preferred embodiment, said stem cells are, or said collection of stem cells comprises, brain, lung, skin, breast, hair follicle, connective tissue, uterus, bone marrow, eye, or heart stem cells that comprise Lgr6 in their cell membrane.

In a further preferred embodiment, said stem cells are, or said collection of stem cells comprises, brain, breast, skin, connective tissue, uterus, or hair follicle stem cells that comprise Lgr5 as well as Lgr6 in their cell membrane.

In yet another embodiment, the invention provides stem cells, or a collection of stem cells wherein at least 50%, preferably at least 60%, more preferably at least 70%, more preferably at least 80%, more preferably at least 90%, more preferably at least 95% of the cells are Lgr5 or 6 positive, pluripotent stem cells, obtainable by a method according to the invention, i.e.

(i) a method for obtaining (or isolating) stem cells comprising

-   -   optionally preparing a cell suspension from a normal tissue or         organ sample     -   contacting said cell suspension with an Lgr5 and/or 6 binding         compound     -   identify or obtaining the cells bound to said binding compound     -   optionally isolating the stem cells from said binding compound,         and/or         (ii) a method for maintaining or culturing tissue stem cells,         comprising providing tissue stem cells with an Lgr5 and/or 6         ligand or a small molecule agonist of Lgr5 and/or 6.

The stem cells, or the collection of stem cells, isolated according to the invention can be used as a therapeutic agent for the treatment of diseases in which the corresponding tissue has been affected. However, the obtained stem cells are also very useful for other purposes.

In yet another useful embodiment, the invention provides the use of stem cells, or a collection of stem cells, as obtained by any of the herein described methods, in the preparation of a medicament for treating damaged or diseased tissue.

Preferably said stem cells are human stem cells. Even more preferably the acceptor is human as well. Table 2 provides an overview of different stem cells and the diseases in which they can therapeutically be used.

TABLE 2 Therapeutic applications for use of Lgr5⁺ and/or Lgr6⁺ stem cells stem cell Therapeutic application brain Brain damage such as stroke and traumatic brain injury. Degenerative diseases such as Alzheimer's, Parkinson, Huntington's kidney Chronic or acute kidney failure liver Chronic liver failure, for instance due to damage by infectious agents, chemicals including alcohol or metabolic disorders lung COPD, fibrosis retina Blindness and vision impairments due to defects in the retina stomach Pernicious anemia Intestinal, Crohn's disease, tissue damage resulting from colon, rectal, and chemotherapy or other toxic agents, colorectal pancreas Diabetes testis Sterility breast Breast reconstruction hair follicle Baldness heart Heart disease such as congestive heart failure ovary Sterility Skin Skin grafting Adrenal medulla Addison's Disease

Hence, the invention provides a use of stem cells, or a collection of stem cells, as obtained by any of the herein described methods, in the preparation of a medicament for treating damaged or diseased tissue,

-   -   wherein said stem cells are intestinal stem cells and wherein         said tissue is damage to the intestinal epithelium, damage to         the liver or damage to the pancreas or     -   wherein said stem cells are retina stem cells and wherein tissue         damage is damaged retina; such an approach is useful in the         treatment of blindness due to defects in the retina; or     -   wherein said stem cells are brain stem cells; or     -   wherein said stem cells are breast stem cells; or     -   wherein said stem cells are hair follicle stem cells and the         damages tissue are hair follicles; such an approach is extremely         useful in the treatment of baldness and involves isolating of         follicle stem cells by the herein described method, multiplying         the obtained stem cells and implanting the new follicles into         the scalp; or     -   wherein said stem cells are stomach stem cells; or     -   wherein said stem cells are liver stem cells; or     -   wherein said stem cells are ovarian stem cells; or     -   wherein said stem cells are skin stem cells for providing skin         grafts; or     -   wherein said stem cells are any of the cells mentioned in Table         2 and the disease to be treated is mentioned as the         corresponding therapeutic application in Table 2, for example         the stem cells are retina stem cells and the disease is         blindness due to defects in the retina.

Gene therapy can additionally be used in a method directed at repairing damaged or diseased tissue. Use can, for example, be made of an adenoviral or retroviral gene delivery vehicle to deliver genetic information (like DNA and/or RNA) to stem cells. A skilled person can replace or repair particular genes targeted in gene therapy. For example, a normal gene may be inserted into a nonspecific location within the genome to replace a nonfunctional gene. This approach is common. In yet another example, an abnormal gene could be swapped for a normal gene through homologous recombination or an abnormal gene could be repaired through selective reverse mutation, which returns the gene to its normal function. A further example is altering the regulation (the degree to which a gene is turned on or off) of a particular gene. Preferably, the stem cells are ex vivo treated by a gene therapy approach and are subsequently transferred to the mammal (preferably a human being) in need of treatment.

Thus, the invention also provides a method for modifying a genomic sequence of a stem cell, comprising providing a collection of stem cells according to a method of the invention, contacting said collection with a nucleic acid to modify a genomic sequence, and isolating a stem cell in which a genomic sequence has been modified. The invention further provides a method for modifying a genomic sequence of a tissue cell comprising providing a collection of tissue cells in vitro with a nucleic acid sequence for modifying said genomic sequence, further comprising isolating a stem cell from said collection of tissue cells according to a method of the invention.

The invention further provides isolated, genomicly modified stem cells obtainable by a method of the invention, and wherein at least 50%, preferably at least 60%, more preferably at least 70%, more preferably at least 80%, more preferably at least 90%, more preferably at least 95% of the cells are pluripotent stem cells which can retain an undifferentiated phenotype. The invention further provides isolated, genomicly modified stem cells obtainable by a method of the invention, and wherein at least 50%, preferably at least 60%, more preferably at least 70%, more preferably at least 80%, more preferably at least 90%, more preferably at least 95% of the cells are adult and/or tissue stem cells as defined herein.

In yet another useful embodiment, the invention provides the use of stem cells as obtained by any of the herein described methods, in the preparation of a medicament for treating damaged or diseased tissue, further comprising genetically modifying said stem cells preferably ex vivo and/or preferably by a gene therapy approach. The invention further provides a composition for treating tissue or organ damage comprising isolated genomicly modified stem cells according to the invention.

In yet an alternative embodiment, the invention provides a composition for treating tissue damage comprising tissue stem cells obtainable by a method according to the invention, i.e.

(i) a method for obtaining (or isolating) stem cells comprising

-   -   optionally preparing a cell suspension from a tissue or organ         sample     -   contacting said cell suspension with an Lgr5 and/or 6 binding         compound     -   identify or obtaining the cells bound to said binding compound     -   optionally isolating the stem cells from said binding compound,         and/or         (ii) a method for maintaining or culturing tissue stem cells,         comprising providing tissue stem cells with an Lgr5 and/or 6         ligand or a small molecule agonist of Lgr5 and/or 6.

Stem cells of the invention are also very useful for research purposes. Examples of suitable research purposes are further identification of stem cell markers or the development of gene therapy with the stem cells of the invention as a target or any other research purpose.

The invention further provides a use of Lgr5 and/or 6 as a marker for the isolation of tissue stem cells as well as the use of an Lgr5 and/or 6 binding compound for the isolation of tissue stem cells.

The invention further provides a method for treating an individual in need thereof comprising administering to said individual a sufficient amount of stem cells obtainable/obtained by a method according to the invention.

In a further embodiment, the invention provides a recombinant animal comprising a first reporter gene under control of a Lgr5 or Lgr6 promoter such that the reporter gene product is expressed in cells expressing Lgr5 or Lgr6, a sequence encoding a regulatable protein being in an operable linkage with the first reporter gene such that the regulatable protein is co-expressed with the first reporter gene product in cells expressing Lgr5 or Lgr6, and a second reporter gene that is expressed upon activation of the regulatable protein.

A recombinant animal of the invention allows staining of tissue or organ stem cells with said first reporter, and allows staining of non-stem cells daughter cells such as committed or differentiated daughter progenitor cells with the second reporter gene product after activation of the regulatable protein.

A reporter gene is a gene that encodes a product that can readily be assayed. Reporter genes are typically used to determine whether a particular nucleic acid construct has been successfully introduced into a cell, organ or tissue and/or to specifically detect the cell in which the reporter gene has been introduced and is expressed. The expression product is typically unique in the sense that non modified cells or cells that do not express the reporter gene are not specifically detected. A reporter gene is also referred to as a marker gene. When two or more reporter genes are used, the different reporter genes are typically not the same, in the sense that their expression products can easily be distinguished from each other. Thus a first and a second reporter gene are typically not the same. A regulatable protein as used herein is a protein that, upon the presence of a signal, alters its function. Many different regulatable proteins have been identified and/or artificially generated. A well known example is the tet-repressor system where the presence or absence of tetracycline or an analogue thereof regulates the activity of the tet-operon by regulating the binding capacity of the tet-repressor protein to the tet-repressor binding sequence. In this example the tet-repressor protein is the regulatable protein and the presence or absence of tetracycline is the signal. Although the tet-repressor system is well known, there are many other regulatable proteins.

Co expression of two or more proteins in a cell is currently very common. Fusion proteins can be generated. Preferably a multi-cistron is used. This is currently typically achieved using at least one so-called internal ribosomal entry site (IRES). Alternative methods include the use of reinitiation sites and/or alternative splicing of an RNA containing two or more open reading frames.

The invention also provides a recombinant stem cell comprising a first reporter gene under control of a Lgr5 or Lgr6 promoter such that the reporter gene product is expressed in cells expressing Lgr5 or Lgr6, a sequence encoding a regulatable protein being in an operable linkage with the first reporter gene such that the regulatable protein is co-expressed with the first reporter gene product in cells expressing Lgr5 or Lgr6, and a second reporter gene that is expressed upon activation of the regulatable protein.

Said stem cell can be generated from an isolated stem cell, or preferably is isolated from a recombinant animal according to the invention.

Said regulatable protein preferably is CRE-ERT2, which can be activated by administration of an estrogen or analogue thereof such as tamoxifen or 4-hydroxytamoxifen. In this preferred embodiment, the expression of the second reporter gene is regulated by activated CRE-ERT2 through the removal of a repressor sequence that prevents expression of the second reporter gene in the inactive state. In a preferred embodiment, said first reporter gene product is a fluorescent protein such as green fluorescent protein, or more preferred enhanced green fluorescent protein. In a further preferred embodiment, said second reporter gene comprises LacZ, encoding beta-galactosidase which can be identified through provision of a suitable substrate such as X-gal. Said second reporter gene is preferably inserted into a genomic region that provides robust, prolonged expression of the transgene after activation, such as the ROSA locus if the transgenic animal is a mouse.

In a preferred embodiment the invention provides a recombinant animal comprising the nucleic acids as specified in the examples in the context of the recombinant animal for tracing stem cells described therein.

In a preferred embodiment said recombinant animal is a non-human animal. Preferably a mammal, more preferably a rodent. More preferably a rat or a mouse.

The invention further provides the use of a recombinant animal or a recombinant stem cell according to the invention for tracing stem cells and descendants of a stem cell.

The invention also provides a method for identifying descendants of a stem cell, comprising providing a recombinant animal or recombinant stem cell according to the invention, activating the regulatable protein, and identifying cells that do not express Lgr5 and/or 6 and the first reporter, and express the second reporter protein.

The present inventors disclose that the expression of Lgr5 (also known as Grp49) as well as the expression of Lgr6 not only mark adult stem cells, but also mark cancer stem cells in multiple different tumors.

In yet another embodiment, the invention provides a method for obtaining (or isolating) cancer stem cells comprising

-   -   optionally preparing a cell suspension from a solid or liquid         tumor sample     -   contacting said cell suspension with an Lgr5 and/or 6 binding         compound     -   identify or obtaining the cells bound to said binding compound     -   optionally isolating the cancer stem cells from said binding         compound.

Preferably said cancer stem cells are involved in intestinal cancer, including colon, rectal and colorectal cancer, skin cancer such as basal cell carcinoma, esophageal cancer, breast cancer, prostate cancer, medulloblastoma and other brain cancers, liver cancer, stomach cancer, retina, head and neck cancer, testicular cancer, hair follicle, ovarian cancer, adrenal medulla cancer (pheochromocytoma) or lung cancer. Thus, in a preferred embodiment, said cancer stem cells are intestinal cancer stem cells, including colon-, rectal- and colorectal cancer stem cells, skin cancer stem cells such as basal cell carcinoma stem cells, esophageal cancer stem cells, breast cancer stem cells, prostate cancer stem cells, medulloblastoma stem cells and other brain cancer stem cells, liver cancer stem cells, stomach cancer stem cells, retina stem cells, head and neck cancer stem cells, testicular cancer stem cells, hair follicle cancer stem cells, ovarian cancer stem cells, pheochromocytoma stem cells, or lung cancer stem cells.

As mentioned, there is some confusion in the literature as to the definition of a cancer stem cell. Herein, we follow the consensus reached at a recent AACR workshop (14), which states that the cancer stem cell “is a cell within a tumor that possesses the capacity to self-renew and to cause the heterogeneous lineages of cancer cells that comprise the tumor. Cancer stem cells can thus only be defined experimentally by their ability to recapitulate the generation of a continuously growing tumor”. Alternative terms in the literature include tumor-initiating cell and tumorigenic cell. Assays for cancer stem cell activity preferably need to address the potential of self-renewal and of tumor propagation. The gold-standard assay currently is serial xeno-transplantation into immunodeficient mice.

A solid tumor sample is for example obtained via biopsy or surgical techniques and a liquid tumor sample is for example obtained by taking a blood, urine, cerebrospinal fluid or lymph sample from a mammal, preferably a human.

The tissue or organ that is sampled is for example the colon, a breast, prostate, brain, liver, stomach or lung.

For information in respect of Lgr5 or 6, the earlier parts of this application can be considered.

In a preferred embodiment, the invention provides a method for obtaining (or isolating) cancer stem cells, or a collection of cancer stem cells, comprising

-   -   optionally preparing a cell suspension from a solid or liquid         tumor sample     -   contacting said cell suspension with an Lgr5 and/or 6 binding         compound     -   identify or obtaining the cells bound to said binding compound     -   optionally isolating the cancer stem cells from said binding         compound,         wherein said cancer stem cells are mammalian, preferably human,         cancer stem cells, and wherein the collection of cancer stem         cells comprises at least 50% cancer stem cells that are able to         recapitulate the generation of a continuously growing tumor. In         a preferred embodiment said collection of cancer stem cells         comprises at least 60% cancer stem cells, preferably at least         70% cancer stem cells, more preferably 80% cancer stem cells,         more preferably 90% cancer stem cells, more preferably 95%         cancer stem cells that are able to recapitulate the generation         of a continuously growing tumor.

Bone marrow and (cord) blood can be considered natural cell suspensions. From solid tumors, cell suspensions can be obtained for instance by mechanical disruption of organ tissue into small fragments. These fragments can then optionally be further segregated into single cells by chemicals such as EDTA and/or by enzymatic digestion with for instance the enzyme preparations dispase, collagenase or pancreatin. The procedure can involve tissue or cell culture before, during or after the disruption and/or enzymatic digestion procedures.

When a cell suspension is already available this step of the method can be omitted (optional feature).

As it is not always necessary to isolate the cancer stem cells from the used binding compound, said step is presented as an optional feature in the claim. When it is necessary to isolate the cancer stem cells from the Lgr5 or 6 binding compound, this can be performed by multiple methods well known to the skilled person. Suitable examples are (mechanical) agitation, enzymatic digestion, addition of excess binding compound or a derivative thereof, elution by changing pH or salt concentration.

Now that the inventors have shown that Lgr5 or 6 are markers for cancer stem cells, compounds that are capable of binding to Lgr5 or 6 (i.e. Lgr5 or 6 binding compounds) can be used to identify, mark and isolate cancer stem cells.

One suitable example of an Lgr5 or 6 binding compound is an antibody or an antibody derivative or an antibody fragment capable of binding to Lgr5 or 6, i.e. an antibody or derivative or fragment thereof that has affinity for Lgr5 or 6. As Lgr5 and 6 are transmembrane surface proteins, such an antibody or a derivative or a fragment thereof preferably has affinity for the part of the protein facing externally, i.e. binds to any extracellular part of said protein.

In a preferred embodiment, said antibody or an antibody derivative or an antibody fragment has a high affinity for Lgr5 and/or 6, i.e. an affinity with a Kd of at least 10⁻⁷. Preferably the affinity is ≤10⁻⁹. However, affinities of around 10⁻⁸ can also be used.

Hence, in a preferred embodiment, the invention provides a method for obtaining (or isolating) cancer stem cells comprising

-   -   optionally preparing a cell suspension from a solid or liquid         tumor sample     -   contacting said cell suspension with an Lgr5 and/or 6 binding         compound     -   identify or obtaining the cells bound to said binding compound     -   optionally isolating the cancer stem cells from said binding         compound,         wherein said Lgr5 or 6 binding compound is an antibody or an         antibody derivative or an antibody fragment capable of binding         to Lgr5 or 6.

Antibodies or their derivatives or their fragments can be provided by methods that are well known to the person skilled in the art and include the hybridoma technique, single chain-antibody/phage display technology.

As non-limiting examples, the experimental part describes Lgr5-specific and Lgr6-specific antibodies. A method according to the invention, wherein an antibody as depicted in Table 4 or 5 is used is therefore also herewith provided, as well as a method according to the invention, wherein an antibody or an antibody derivative or an antibody fragment is used which comprises at least one CDR sequence as depicted in FIG. 27. Preferably, said antibody or antibody derivative or antibody fragment comprises a CDR1 sequence and a CDR2 sequence and a CDR3 sequence of a light chain and/or heavy chain depicted in FIG. 27.

Examples of suitable antibody fragments are scFv, Fab. Examples of suitable derivatives are chimeric antibodies, nanobodies, bifunctional antibodies or humanized antibodies. In yet another preferred embodiment, the used antibody is a monoclonal antibody.

Another example of an Lgr5 or 6 binding compound is an Lgr5 or 6 ligand which can be used unmodified, but can also be produced and/or used as a fusion protein or can be coupled to a second moiety to allow cell separation.

In a preferred embodiment, the invention therefore provides a method for obtaining (or isolating) cancer stem cells comprising

-   -   optionally preparing a cell suspension from a solid or liquid         tumor sample     -   contacting said cell suspension with an Lgr5 and/or 6 binding         compound     -   identify or obtaining the cells bound to said binding compound     -   optionally isolating the cancer stem cells from said binding         compound,         wherein said Lgr5 or 6 binding compound is an Lgr5 or 6 ligand.

The person skilled in the art is very well capable of producing an Lgr5 or 6 ligand fusion protein, for example via standard molecular biology techniques.

A suitable example of an Lgr5 or 6 ligand is a member of the insulin peptide family, such as Insl5 or relaxin3. Another suitable example is a cysteine-knot protein such as Noggin, Gremlin, Dan, or Cerberus. Based on the known and published nucleotide and amino acid sequences of these ligands, the preparation of a fusion protein is well within the abilities of the person skilled in the art.

Preferably the second moiety introduces a feature which allows for easy identification and tracing of the fusion protein, for example a protein (fragment) such as the antibody Fc tail or Staphylococcal protein A or Glutathion-S-transferase, a short antigenic peptide tag such as the Myc, FLAG or HA tag or an oligomeric Histidine-tag, an enzymatic tag such as Alkaline Phosphatase, a fluorescent protein tag (such as Green Fluorescent Protein). Small chemical moieties can also be coupled to the ligand for cancer stem cell identification and/or isolation. These moieties can be recognized and bound by specific antibodies, or can have specific affinity for a material to be used in cell separation, or can for instance be fluorescent, radioactive or magnetic properties. In an even more preferred embodiment, the second part of the fusion protein is linked to said Lgr5 or 6 ligand via a spacer. Even more preferable, said spacer comprises an enzyme digestible sequence. This allows for an easy separation of the second moiety and the Lgr5 or 6 ligand.

Yet another example of an Lgr5 or 6 binding compound is a small compound that has affinity for Lgr5 or 6.

In a preferred embodiment, the invention thus provide a method for obtaining (or isolating) cancer stem cells comprising

-   -   optionally preparing a cell suspension from a solid or liquid         tumor sample     -   contacting said cell suspension with an Lgr5 and/or 6 binding         compound     -   identify or obtaining the cells bound to said binding compound     -   optionally isolating the cancer stem cells from said binding         compound,         wherein said Lgr5 and/or 6 binding compound a small molecule         with affinity for Lgr5 and/or 6. Such a small molecule is for         example a synthetic peptide or a small chemical compound.

In a preferred embodiment, the affinity of said small molecule for Lgr5 or 6 is a high, i.e. an affinity with a Kd of at least 10⁻⁷.

Such a small molecule is optionally coupled to a second moiety that introduces a feature which allows for easy identification and tracing of the fusion protein, for example a protein (fragment) such as the antibody Fc tail or Staphylococcal protein A or Glutathion-S-transferase, a short antigenic peptide tag such as the Myc, FLAG or HA tag or an oligomeric Histidine-tag, an enzymatic tag such as Alkaline Phosphatase, a fluorescent protein tag such as Green Fluorescent Protein).

Depending on the desired cancer stem cell and the now known presence or absence of Lgr5 or 6, a method according to the invention can use at least one, at least two, at least three or even more (different) binding compound(s). Table 3 provides an overview of the presence of absence of Lgr5 or 6 on the different kind of tumors. Based on this Table the person skilled in the art is very well capable of selecting one or multiple target markers and one or multiple corresponding binding compounds and thus capable of obtaining or isolating cancer stem cells.

TABLE 3 The distribution of the stem cell markers Lgr5 and 6 in tumors. Data is derived from comparison of Lgr5 or Lgr6 expression in normal versus tumor tissues by microarray analysis (Genelogic) or by quantitative PCR. Cancer stem Marker cell Lgr5 Lgr6 brain + + kidney − − liver + − lung − + retina + − stomach + − Colon/rectal + + head and neck + + testis + + breast + + hair follicle + + prostate + + ovary + + skin + + leukemia + − chondrosarcoma + + muscle/soft + − tissue uterus + + retinoblastoma − +

If the person skilled in the art wants to obtain breast cancer stem cells, a binding compound of Lgr5 or 6 can be used alone or in any combination thereof, because the breast cancer stem cells comprise both of said markers.

In a preferred embodiment, the invention provides a method for obtaining (or isolating) cancer stem cells comprising

-   -   optionally preparing a cell suspension from a solid or liquid         tumor sample     -   contacting said cell suspension with an Lgr5 and/or 6 binding         compound     -   identify or obtaining the cells bound to said binding compound     -   optionally isolating the cancer stem cells from said binding         compound,         wherein     -   said Lgr5 or 6 binding compound is an Lgr5 binding compound and         wherein said cancer stem cells are brain, liver, retina,         stomach, colon, head and/or neck, testis, prostate, ovary, skin,         hair follicle, leukemia, chondrosarcoma, muscle/soft tissue,         uterus, or breast stem cells; or     -   said Lgr5 or 6 binding compound is an Lgr6 binding compound and         wherein said cancer stem cells are brain, lung, head and/or         neck, testis, breast, hair follicle, skin, prostate,         chondrosarcoma, uterus, retinoblastoma, or ovary stem cells; or     -   said Lgr5 or 6 binding compound is at least one Lgr6 binding         compound in combination with at least one Lgr5 binding compound         and wherein said cancer stem cells are brain, skin, head and/or         neck, testis, breast, prostate, ovary, chondrosarcoma, uterus,         or hair follicle stem cells.

In a preferred embodiment, the invention provides a method for obtaining (or isolating) cancer stem cells comprising

-   -   optionally preparing a cell suspension from a solid or liquid         tumor sample     -   contacting said cell suspension with an Lgr5 and/or 6 binding         compound     -   identify or obtaining the cells bound to said binding compound     -   optionally isolating the cancer stem cells from said binding         compound,         wherein one binding compound is used.

In yet another preferred embodiment, the invention provides a method for obtaining (or isolating) cancer stem cells comprising

-   -   optionally preparing a cell suspension from a solid or liquid         tumor sample     -   contacting said cell suspension with an Lgr5 and/or 6 binding         compound     -   identify or obtaining the cells bound to said binding compound     -   optionally isolating the cancer stem cells from said binding         compound,         wherein at least two different binding compounds are contacted         with said cell suspension. Said two different binding compounds         can be directed against one and the same marker (for example         directed to Lgr5). For example, use can be made of two         antibodies directed to two different epitopes which antibodies         together provide (a preferably essentially complete) capture of         the desired stem cells. However, said two different binding         compounds can also be directed to two different stem cell         markers (for example to Lgr6 and Lgr5). Whenever use is made of         two or three or even more binding compounds, said binding         compounds may be from the same class of binding compounds (for         example all being antibodies, small molecules or ligand (fusion         proteins)) or may be from different classes of binding compounds         (for example an antibody directed to Lgr6 and a ligand fusion         protein for binding to Lgr5).

In a preferred embodiment, at least two different antibodies or antibody derivatives or antibody fragments capable of binding to Lgr5 and/or 6 are contacted with a cell suspension.

After allowing the binding compounds to interact with the cell suspension (for a certain amount of time or under different conditions such as pH, temperature, salt etc.), subsequent identification of obtained bound complexes is performed. This is for example accomplished by using FACS analysis. Fluorescence-activated cell-sorting (FACS) is a specialised type of flow cytometry. It provides a method for sorting a heterogenous mixture of biological cells into two or more containers, one cell at a time, based upon the specific light scattering and fluorescent characteristics of each cell. It is a useful scientific instrument as it provides fast, objective and quantitative recording of fluorescent signals from individual cells as well as physical separation of cells of particular interest.

In a preferred embodiment, the invention provides a method for obtaining (or isolating) cancer stem cells, or a collection of cancer stem cells, comprising

-   -   optionally preparing a cell suspension from a solid or liquid         tumor sample     -   contacting said cell suspension with an Lgr5 and/or 6 binding         compound     -   identify or obtaining the cells bound to said binding compound     -   optionally isolating the cancer stem cells from said binding         compound,         wherein a FACS is used to identify and sort the cells that bind         to an Lgr5 and/or 6 binding compound, and wherein said         collection comprises at least 50% of cancer stem cells that are         able to recapitulate the generation of a continuously growing         tumor. Preferably, said collection comprises at least 60%, more         preferably at least 70%, more preferably at least 80%, more         preferably at least 90%, more preferably at least 95% of cancer         stem cells that are able to recapitulate the generation of a         continuously growing tumor.

Other options for identification of bound complexes are magnetic bead sorting, (immuno)affinity column cell separation, or (immuno)affinity panning.

For analysis by FACS, the binding compound is preferably provided with a fluorescence label, for analysis by magnetic bead sorting the binding compound is preferably provided with magnetic beads (for example an antibody-coated magnetic bead).

In yet another embodiment, the invention provides (a collection of) cancer stem cells comprising Lgr5 and/or 6 embedded in their cell membrane, wherein said collection comprises at least 50% of cancer stem cells that are able to recapitulate the generation of a continuously growing tumor. In a preferred embodiment said collection comprises at least 60% pure cancer stem cells, preferably at least 70% pure cancer stem cells, more preferably at least 80% pure cancer stem cells, more preferably at least 90% pure cancer stem cells, more preferably at least 95% pure cancer stem cells. More preferably said collection consists of (cancer) stem cells with the indicated purity. Such a collection of cancer stem cells is for example obtained by a method as described herein, i.e. a method for obtaining (or isolating) cancer stem cells comprising

-   -   optionally preparing a cell suspension from a solid or liquid         tumor sample     -   contacting said cell suspension with an Lgr5 and/or 6 binding         compound     -   identify or obtaining the cells bound to said binding compound     -   optionally isolating the cancer stem cells from said binding         compound.

Examples of cancer stem cells that can be obtained via the above mentioned methods are colon, rectal, intestine, skin, retina, brain, breast, testis, hair follicle, stomach, head and/or neck, liver, lung, prostate, esophagus, adrenal medulla, heart, or ovarian cancer stem cells.

If necessary, said cancer stem cells are maintained or multiplied (expanded) by culturing said cells in the presence of an Lgr5 and/or 6 ligand under appropriate environmental conditions (for example pH and temperature). A suitable example of an Lgr5 or 6 ligand is a member of the insulin peptide family, such as Insl5 or relaxin3. Another suitable example is a cysteine-knot protein such as Noggin, Gremlin, Dan, or Cerberus.

Hence, in yet another embodiment, the invention provides a method for maintaining or culturing cancer stem cells, comprising providing cancer stem cells with an Lgr5 and/or 6 ligand or a small binding molecule of Lgr5 or 6.

The invention further provides a collection of (isolated) cancer stem cells of the invention further comprising an Lgr5 and/or Lgr6 binding compound associated with Lgr5 and/or Lgr6 expressed by said cancer stem cells. The invention further provides a culture of (isolated) cancer stem cells comprising an Lgr5 and/or Lgr6 binding compound. Preferably said Lgr5 and/or Lgr6 binding compound is a specific Lgr5 and/or Lgr6 binding antibody or a fragment or derivative thereof.

In a preferred embodiment, the invention provides a recombinant tumor stem cell, isolated according to a method of the invention, comprising a reporter gene under control of a Lgr5 or Lgr6 promoter such that the reporter gene product is expressed in cells expressing Lgr5 or Lgr6. A reporter gene construct, in which the reporter gene is operably linked to a Lgr5 or Lgr6 promoter, can be inserted into the genome of an isolated tumor stem cell. Alternatively, said reporter gene construct can be provided, for example, through infection of a tumor stem cell with an adenoviral vector comprising the reporter gene construct. Methods for inserting a reporter gene construct into the genome of a cell are known to a skilled person and include random insertion, for example by insertion of a retrovirus comprising the reporter gene construct, or through homologous recombination.

In a further preferred embodiment, the invention provides a recombinant stem cell comprising a first reporter gene under control of a Lgr5 or Lgr6 promoter such that the reporter gene product is expressed in cells expressing Lgr5 or Lgr6, a sequence encoding a regulatable protein being in an operable linkage with the first reporter gene such that the regulatable protein is co-expressed with the first reporter gene product in cells expressing Lgr5 or Lgr6, and a second reporter gene that is expressed upon activation of the regulatable protein.

Said first reporter gene product preferably is a fluorescent protein such as green fluorescent protein, or more preferred enhanced green fluorescent protein. Said regulatable protein preferably is CRE-ERT2. The second reporter gene preferably comprises LacZ.

Isolated (and optionally cultured) cancer stem cells are for example useful for the further analysis of such cells on for example biochemical, molecular biology or marker level.

Moreover, isolated cancer stem cells are also very useful in the identification of compounds that can be used in cancer treatment, especially cancer stem cell therapy. Based on the knowledge that Lgr5 and/or 6 are embedded in the cell membrane of cancer stem cells, compounds capable of inhibiting, blocking or binding to Lgr5 and/or 6 can be designed and prepared. Such compounds can subsequently be tested for their ability to kill or functionally block or inhibit cancer stem cells comprising Lgr5 and/or 6 in their cell membrane.

Recombinant tumor stem cells according to the invention are particularly preferred for the identification of compounds, because their presence can readily be monitored after addition of a compound. Said recombinant tumor stem cells are suited for use in assays such a high throughput assays, where multiple compounds are tested in a cost-efficient manner.

In another embodiment, the invention thus provides a method for testing the effect of a possible anti cancer stem cell compound comprising contacting (treating) a set of cancer stem cells according to the invention in vitro with said possible anti cancer stem cell compound and testing whether said treated cancer stem cells are capable of generating a continuously growing tumor and wherein said possible cancer stem cell compound is preferably designed as an Lgr5 or 6 inhibitor or as an Lgr5 or 6 binding compound.

In yet another embodiment, the invention provides a method for testing the effect of a possible anti cancer stem cell compound comprising contacting a collection of cancer stem cells according to the invention in vitro with said possible anti cancer stem cell compound and testing whether said treated cancer stem cells are capable of generating a continuously growing tumor, further comprising contacting said possible anti cancer stem cell compound with a tissue of organ stem cell and selecting a compound that specifically effects tumour stem cells.

The cancer stem cells used in this method comprise Lgr5 and/or 6 in their cell membrane or are obtainable by a method for obtaining (or isolating) cancer stem cells comprising

-   -   optionally preparing a cell suspension from a solid or liquid         tumor sample     -   contacting said cell suspension with an Lgr5 and/or 6 binding         compound     -   identify or obtaining the cells bound to said binding compound     -   optionally isolating the cancer stem cells from said binding         compound.

The to be tested compounds can for example be obtained from a (small) compound library or can be specifically designed based on the (structural) knowledge of Lgr5 or 6 or on the (structural) knowledge of a (natural) ligand of Lgr5 or 6.

The anti cancer stem cell compounds will be discussed in more detail below.

In yet a further embodiment, the invention provides an Lgr5 or 6 inhibitor or an Lgr5 or 6 binding compound. Preferably such an inhibitor or binding compound is obtainable by a method for testing the effect of a possible anti cancer stem cell compound comprising contacting (treating) a set of cancer stem cells according to the invention in vitro with said possible anti cancer stem cell compound and testing whether said treated cancer stem cells are capable of generating a continuously growing tumor and wherein said possible cancer stem cell compound is preferably, but nor necessarily, designed as an Lgr5 or 6 inhibitor or as an Lgr5 or 6 binding compound.

A first example of an Lgr5 or 6 inhibitor is an inhibitor of Lgr5 or 6 protein. Preferably said Lgr5 or 6 protein inhibitor is an antibody or antibody derivative or antibody fragment capable of binding to Lgr5 or 6 and more preferably capable of binding to the part of Lgr5 or 6 that is exposed on the outside of the cancer stem cell. In yet another preferred embodiment, said antibody or antibody derivative or antibody fragment binds to said Lgr5 or 6 protein and functionally blocks said Lgr5 or 6 protein by preventing the binding of a natural ligand of Lgr5 or 6. In one embodiment, said antibody or antibody derivative or antibody fragment comprises at least one CDR sequence as depicted in FIG. 27. Preferably, said antibody or antibody derivative or antibody fragment comprises a CDR1 sequence and a CDR2 sequence and a CDR3 sequence of a light chain and/or a heavy chain depicted in FIG. 27. In a further embodiment, said antibody is an antibody as depicted in Table 4 or 5.

Examples of suitable antibody fragments are scFv and Fab. Examples of suitable derivatives are chimeric antibodies, nanobodies, bifunctional antibodies or humanized antibodies.

In yet another preferred embodiment, the used antibody is a monoclonal antibody.

Another example of an Lgr5 or 6 protein inhibitor is a small molecule that interferes with the biological activity of Lgr5 or 6. Such a small molecule can be a chemical compound as well as a small protein and is typically designed on the basis of structure-function analysis of Lgr5 or 6. Analysis can comprise crystal structure analysis of Lgr5 or 6. Small molecules libraries can be screened or compounds can be designed and subsequently screened. A small molecule inhibitor can also be designed based on the structure of a (natural) ligand of Lgr5 or 6.

Yet another example of an Lgr5 or 6 inhibitor is an inhibitor of the mRNA transcripts of Lgr 5 or 6. One example of an inhibitor of Lgr5 or 6 transcript are antisense molecules. Antisense drugs are complementary strands of small segments of mRNA. Such an antisense molecule binds to the mRNA of Lgr5 or 6 and inhibits (at least in part) Lgr5 or 6 protein production. Another example of an inhibitor of Lgr5 or 6 transcript relate to RNA interference (RNAi) molecules such as siRNA molecules.

Besides the option that an antibody or antibody derivative or antibody fragment binds to Lgr5 or 6 and functionally blocks Lgr5 or 6 (as described above), said antibody or antibody derivative or antibody fragment can also bind to Lgr5 or 6 without functionally blocking the Lgr5 or 6 activity. Such an antibody or antibody derivative or antibody fragment is preferably coupled to another compound (i.e. another moiety) that is capable of functionally inhibiting a cancer stem cell. An example of such another compound is a toxin. Hence, the invention also provides a cancer stem cell inhibitor, wherein said inhibitor comprises a first part that is capable of binding to Lgr5 or 6 and a second part that provides for cancer stem cell dysfunction. Preferably, said first part is an antibody or antibody derivative or antibody fragment binds to Lgr5 or 6 (preferably without influencing the function of Lgr5 or 6) and said second part is a toxin. In this embodiment Lg5 or 6 is used as a target to deliver a cytotoxic compound to a cancer stem cell.

Thus, the invention also provides a binding compound according to the invention that is linked to a toxic agent or linked to an enzyme capable of converting a prodrug to a toxic agent. For example, the antibody or derivative or fragment thereof is linked to a toxic agent to form an immunoconjugate. Said toxic agent includes a radioisotope and a toxic drug which is ineffective when administered systemically alone. By combining the targeting-specificity of a binding compound of the invention to Lgr 5 and/or 6-expressing tumor stem cells with the killing power of a toxic effector molecule, immunoconjugates permit sensitive discrimination between target and normal tissue, resulting in fewer toxic side effects than most conventional chemotherapeutic drugs. Examples of prodrugs that can be targeted to Lgr 5 or 6-expressing tumor stem cells comprise benzoic acid mustard whereby the antibody is conjugated to carboxypeptidase G2; nitrogen mustardcephalosporin-p-phenylenediamine whereby the antibody is conjugated to beta-lactamase; and cyanophenylmethylbeta-D-gluco-pyranosiduronic acid, whereby the antibody is conjugated to beta-glucosidase.

The invention further provides a use of a binding compound according to the invention as a medicament for treatment of cancer. In a preferred embodiment said binding compound comprises an antibody specific for Lgr5 and/or Lgr6 or an Lgr5 or 6 binding fragment or derivative thereof. In a preferred embodiment said antibody is a human, humanized or deimmunised anti Lgr5 and/or Lgr6 antibody as described herein. In a preferred embodiment said binding compound is specific for human Lgr5 and/or human Lgr6. Preferably said antibody is a monoclonal antibody. In one embodiment, said binding compound is an antibody or antibody derivative or antibody fragment which comprises at least one CDR sequence as depicted in FIG. 27. Preferably, said antibody or antibody derivative or antibody fragment comprises a CDR1 sequence and a CDR2 sequence and a CDR3 sequence of a light chain and/or a heavy chain depicted in FIG. 27. In a further embodiment, said binding compound is an antibody as depicted in Table 4 or 5. In a preferred embodiment, a binding compound according to the invention is linked to a toxic agent or linked to an enzyme capable of converting a prodrug to a toxic agent.

In yet another embodiment, the invention provides a cancer stem cell inhibitor comprising an Lgr5 or 6 ligand preferably coupled to another compound (i.e. another moiety) that is capable of functionally inhibiting a cancer stem cell. An example of such another compound is a toxin. Examples of an Lgr5 or 6 ligand are ligands that are a member of the insulin peptide family. Suitable examples are Insl5 and relaxin3. Another suitable example is a cysteine-knot protein such as Noggin, Gremlin, Dan, or Cerberus. Moreover, a natural ligand can be modified such that it permanently blocks Lgr5 or 6 activity.

All the above mentioned Lgr5 or 6 protein inhibitors, inhibitors of the mRNA transcripts of Lgr5 or 6, as well as the described cancer stem cell inhibitors are very useful for therapeutic cancer therapy approaches.

In yet another embodiment, the invention provides the use of at least one Lgr5 or 6 inhibitor or at least one Lgr5 or 6 binding compound as described herein (e.g. an Lgr5 or 6 protein inhibitor or an inhibitor of the mRNA transcripts of Lgr5 or 6 or a cancer stem cell inhibitor) for the manufacture of a medicament for the treatment of cancer.

Preferably, said inhibitors are obtainable according to a method of the invention, i.e. a method for testing the effect of a possible anti cancer stem cell compound comprising contacting (treating) a set of cancer stem cells according to the invention in vitro with said possible anti cancer stem cell compound and testing whether said treated cancer stem cells are capable of generating a continuously growing tumor and wherein said possible cancer stem cell compound is preferably designed as an Lgr5 or 6 inhibitor or as an Lgr5 or 6 binding compound. In a preferred embodiment, use is made of an Lgr5 or 6 inhibitor or an Lgr5 or 6 binding compound.

The invention further provides a method for reducing or inhibiting tumor maintenance potential of a tumor, comprising providing said tumor with a compound that is designed as an Lgr5 and/or 6 inhibitor, or preferably that is capable of binding to Lgr5 and/or 6.

An anti cancer stem cell therapy is very useful to eradicate the part of the tumor that maintains the tumor and is involved in invasive growth and metastasis. Although such an approach is considered to be a very effective cancer therapy, improved or increased results can be obtained by combining the anti cancer stem cell therapy with conventional cancer therapy.

In a preferred embodiment, the invention provides the use of at least one Lgr5 or 6 inhibitor or at least one Lgr5 or 6 binding compound as described herein (e.g. an Lgr5 or 6 protein inhibitor or an inhibitor of the mRNA transcripts of Lgr5 or 6 or a cancer stem cell inhibitor) for the manufacture of a medicament for the treatment of cancer, further comprising general anti-cancer therapy. Examples of said general (or conventional) anti-cancer therapy are radiation, chemotherapy, antibody-based therapy or small molecule based treatments. Combined treatment leads to an approach of killing the minority cancer stem cell population as well as the bulk of the tumor.

In another preferred embodiment, the invention provides the use of at least one Lgr5 or 6 inhibitor or at least one Lgr5 or 6 binding compound as described herein (e.g. an Lgr5 or 6 protein inhibitor or an inhibitor of the mRNA transcripts of Lgr5 or 6 or a cancer stem cell inhibitor) for the manufacture of a medicament for the treatment of cancer, wherein cancer stem cells are involved in intestinal cancer, colon cancer, rectal cancer, colorectal cancer, skin cancer, esophageal cancer, breast cancer, prostate cancer, medulloblastoma or other brain cancers, liver cancer, stomach cancer, hair follicle cancer, retinal cancer, pheochromcytoma, head and neck cancer, testicular cancer, ovarian cancer, basel cell carcinoma of the skin or lung cancer. In this respect, “involved” means sustaining and/or maintaining and/or expanding.

Preferably, the treatment with at least one Lgr5 and/or 6 inhibitor or at least one Lgr5 and/or 6 binding compound is initiated before, after or during said conventional cancer therapy.

Although treatment with at least one Lgr5 and/or 6 inhibitor or at least one Lgr5 and/or 6 binding compound is considered to be effective, treatment with multiple inhibitors and/or binding compounds can provide improved results. This is especially true if the to be treated cancer stem cell comprises two, three or even more different Lgr proteins embedded in its cell membrane.

In a preferred embodiment, the invention provides the use of at least one Lgr5 and/or 6 inhibitor or at least one Lgr5 and/or 6 binding compound as described herein (e.g. an Lgr5 or 6 protein inhibitor or an inhibitor of the mRNA transcripts of Lgr5 or 6 or a cancer stem cell inhibitor) for the manufacture of a medicament for the treatment of cancer, wherein at least two Lg5 and/or 6 inhibitors or at least two Lgr5 and/or 6 binding compounds or a combination of at least one Lgr5 and/or 6 inhibitor and at least one Lgr5 and/or 6 binding compound are/is used.

The invention thus provides use of at least two Lgr5 and/or 6 inhibitors or at least two Lgr5 and/or 6 binding compounds or a combination of at least one Lgr5 and/or 6 inhibitor and at least one Lgr5 and/or 6 binding compound for the manufacture of a medicament for the treatment of cancer stem cells. An inhibitor and/or binding compound can, but need not be, directed to one and the same Lgr protein, e.g. a binding compound and an inhibitor against Lgr5. The mixture of at least two Lgr5 or 6 inhibitors or at least two Lgr5 or 6 binding compounds or a combination of at least one Lgr5 or 6 inhibitor and at least one Lgr5 or 6 binding compound is for example directed against Lgr5 and 6. The latter is especially useful in a method for obtaining brain, head and neck, testis, breast, prostate, skin, ovary or hair follicle cancer stem cells.

Another already described useful compound is a stem cell inhibitor comprising an Lgr5 and/or 6 ligand preferably coupled to another compound (i.e. another moiety) that is capable of functionally inhibiting a cancer stem cell. An example of such another compound is a toxin. Examples of an Lgr5 or 6 ligand are ligands that are a member of the insulin peptide family. Suitable examples are Insl5 and relaxin3. Another suitable example is a cysteine-knot protein such as Noggin, Gremlin, Dan, or Cerberus. Such a compound can also be used in a cancer stem cell therapy.

Therefore, the invention provides use of a compound that is capable of binding to a ligand of Lgr5 and/or 6 for the manufacture of a medicament for the treatment of cancer stem cells. Preferably, said ligand is coupled to another compound (i.e. another moiety) that is capable of functionally inhibiting a cancer stem cell, such as a toxin or an enzyme capable of converting a prodrug to a toxic agent. Even more preferably, such a treatment is combined with general cancer therapy, such as radiation, chemotherapy, antibody-based therapy or small molecule based treatments.

In yet another embodiment, the invention provides use of a compound that is capable of binding to a ligand of Lgr5 and/or 6 for the manufacture of a medicament for the treatment of cancer stem cells. Preferably the binding of said compound to an Lgr5 and/or 6 ligand is such that said ligand is no longer capable of binding to Lgr5 and/or 6. An example is an antibody or antibody derivative or antibody fragment that captures a (natural) ligand of Lgr5 and/or 6 and thus prevents the activation of Lgr5 and/or 6.

The invention further provides a composition comprising at least one Lgr5 and/or 6 inhibitor or at least one Lgr5 and/or 6 binding compound or at least one Lgr5 and/or 6 ligand or at least one compound capable of binding to an Lgr5 and/or 6 ligand, preferably all as described herein before. Preferably said composition is a pharmaceutical composition. Such a pharmaceutical composition can further comprise any pharmaceutically acceptable excipient, stabilizer, activator, carrier, permeator, propellant, desinfectant, diluent and/or preservative. A pharmaceutical composition may be in any desired form, e.g. a tablet, infusion fluid, capsule, syrup, etc.

In a further preferred embodiment a (pharmaceutical) composition comprises at least two Lgr5 and/or 6 inhibitors or at least two Lgr5 and/or 6 binding compounds or a combination of at least one Lgr5 and/or 6 inhibitor and at least one Lgr5 and/or 6 binding compound.

Now that the inventors have disclosed that Lgr5 and/or 6 are cancer stem cell markers this further opens possibilities in the field of diagnostics. One can for example use an Lgr5 and/or 6 binding compound to determine the cancer stem cell content of a tumor or to determine the presence or absence of a cancer stem cell in a body fluid such as blood. Preferably, the binding compound has a high affinity for Lgr5 or 6 (i.e. the Kd is at least 10⁷). Suitable binding compounds are an Lgr5 and/or 6 ligand, an antibody or an antibody derivative or an antibody fragment capable of binding to Lgr5 and/or 6, e.g. an antibody or derivative or fragment thereof that has affinity for Lgr5 and/or 6.

The invention thus also provides a method for determining cancer stem cell content of a tumor, comprising contacting said tumor with an Lgr5 and/or 6 binding compound, removing unbound binding compound and determining whether any bound binding compound is present in said tumor.

In a preferred embodiment, said method is an in vitro method. Even more preferably, said binding compound is labeled such that it can be identified. Suitable labels are for example a protein (fragment) such as the antibody Fc tail or Staphylococcal protein A or Glutathion-S-transferase, a short antigenic peptide tag such as the Myc, FLAG or HA tag or an oligomeric Histidine-tag, an enzymatic tag such as Alkaline Phosphatase, a fluorescent protein tag (such as Green Fluorescent Protein). However, it is also possible to use a second compound that has affinity for the binding compound and labeling said second compound with a suitable label (i.e. an indirect analysis).

For in vivo application, the invention further provide use of an Lgr5 and/or 6 binding compound in the preparation of a diagnostic for the diagnosis of cancer stem cell presence and/or content in a tumor.

Said sample is for example obtained from a body fluid or a sample obtained from a solid tumor.

In a preferred embodiment, the invention provides a method for determining cancer stem cell content of a tumor, comprising contacting said tumor with an Lgr5 and/or 6 binding compound and determining whether any bound binding compound is present in said tumor. The invention also provides use of an Lgr5 and/or 6 binding compound in the preparation of a diagnostic for the diagnosis of cancer stem cell presence and/or content in a sample, wherein said binding compound is conjugated to a substance that allows radioactive imaging, positron emission tomography (PET) scanning, magnetic resonance imaging (MRI) scanning, or X-ray/computed tomography (CT) scanning.

The invention further provides a method for determining whether a body fluid comprises a cancer stem cell, comprising

-   -   optionally obtaining a sample from said body fluid     -   contacting said body fluid with an Lgr5 and/or 6 binding         compound     -   removing unbound binding compound     -   detecting any bound complex comprising an Lgr5 and/or 6 binding         compound, and determining the presence of a cancer stem cell         based on the presence of detected bound complex.

Suitable binding compounds are an Lgr5 and/or 6 ligand, an antibody or an antibody derivative or an antibody fragment capable of binding to Lgr5 and/or 6, i.e. an antibody or derivative or fragment thereof that has affinity for Lgr5 and/or 6.

The step of removing any unbound binding compound is for example accomplished by washing with a suitable solution or buffer.

Examples of body fluid are blood, urine, lymph fluid or tears.

In a preferred embodiment, said method is an in vitro method.

Suitable labels have been mentioned above.

The described diagnostic methods are also very useful for determining whether an anti cancer therapy leads to eradication of (at least part of the) cancer stem cells. If for example use is made of general anti cancer therapy (or combined treatment with for example an Lgr5 and/or 6 inhibitor), the effect of said therapy on the cancer stem cell can be determined by determining the presence or absence of cells bearing Lgr5 and/or 6.

In yet another embodiment, the invention provides a method for determining the effectivity of an anti cancer treatment, comprising treating cancer and determining whether cancer stem cells are present comprising contacting said cancer with an Lgr5 and/or 6 binding compound.

Such a method can be performed in vitro as well as in vivo.

Preferably the presence of cancer stem cells is determined before treatment and during or after treatment such that it can determined whether or not the applied treatment results in a changed (preferably decreased) amount of cancer stem cells.

The invention further provides a method for treating an individual in need thereof comprising administering an effective amount of a herein described pharmaceutical composition to said individual and optionally further subjecting said individual to conventional cancer therapy such as radiation or chemotherapy.

The invention will be explained in more detail in the following, non-limiting examples.

FIGURE LEGENDS

FIG. 1. Gpr49/Lgr5 is a Wnt target gene in a human colon cancer cell line and is expressed in mouse crypts. a: Northern blot analysis (upper panel); ethidium bromide-stained gel (lower panel). Lane 1: Control Ls174T-L8 cells. Lane 2: Ls174T cells after 24 hours doxycycline induced Wnt pathway inhibition as in 6 (References 2). Note the strong downregulation of the 4.4 kb Grp49 mRNA upon Wnt pathway inhibition. Lane 3: RNA extracted from isolated mouse small intestinal crypts, which unavoidably suffers from limited degradation resulting in some smearing. Lane 4: RNA extracted from isolated mouse villi. Note the specific expression of Grp49 in mouse crypts. b/c Two overlapping images of an in-situ hybridization performed on small intestines of an APCmin mouse, illustrating the ubiquitous expression of Grp49 at crypt bottoms (examples marked with white arrows) and the expression in the adenoma in the left panel (marked by a broken line).

FIG. 2. Gpr49/Lgr5 expression in cycling Crypt Base Columnar (CBC) cells of the small intestine. a-c, In-Situ hybridization was performed with probes specific for 3 Tcf target genes demonstrating non-overlapping expression patterns on the crypt epithelium. a: Cryptdin specifically marks Paneth cells at the crypt base; b: KIAA0007 marks the TA cells located above the Paneth cells c: Gpr49/Lgr5 is specifically expressed in 4-8 cells intermingled with the Paneth cells at the crypt base. All sense controls were negative (not shown). d: CBC cells (circled) are only poorly visible on heamatoxylin/eosin stained sections. e: CBC cells (circled) are KI67+f: Some CBC cells express the M-phase marker phospho-histidine H3 (circled). g: BrdU incorporation in CBC cells 4 hours after a single dose of BrdU (circled). h: BrdU incorporation in CBC cells after 24 hour continuous BrdU labeling (circled). Black bars: Numbers of BrdU-positive CBC cells per crypt section after 4 hours or 24 hours. White bar: Total number of CBC cells per crypt section assessed by counting LacZ-positive cells in Gpr49-LacZ mice.

FIG. 3. Restricted expression of a GPR49-LacZ reporter gene in adult mice a: Generation of mice carrying lacZ integrated into the last exon of the Gpr49 gene, removing all transmembrane regions of the encoded Gpr49 protein. b-h, Expression of GPR49lacZ in selected adult mouse tissues. b/c: In the small intestine expression is restricted to 6-8 slender cells intermingled with the Paneth cells at the crypt base. d/e: In the colon, expression is confined to a few cells located at the crypt base. f/g: Expression in the stomach is limited to the base of the glands. h: In the mammary glands, expression was evident only in smaller, actively proliferating glands, where it was restricted to basal epithelial cells. i: In the skin, expression occurs in the outer root sheath of the hair follicles in a domain extending from the bulge to the dermal papilla.

FIG. 4. EGFP expression in a GPR49-EGFP-Ires-CreERT2 knock-in mouse faithfully reproduces the GPR49lacZ expression pattern in the intestinal tract. a: Generation of mice expressing EGFP and CreERT2 from a single bicistronic message by gene knock-in into the first exon of Gpr49. b,c,e: Confocal GFP imaging counterstained with the red DNA dye ToPro-3 confirms that Gpr49 expression is restricted to the 6-8 slender cells sandwiched between the Paneth cells at the crypt base of the small intestine. b: Entire crypt-villus unit; c: enlargement of crypt regions; d: Immunohistochemical analysis of EGFP expression in intestinal crypts. e: 2D image of 3D reconstruction supplied as supplemental movie in FIG. 7. f. Confocal imaging of EGFP expression in the colon confirms Gpr49 expression is restricted to a few cells located at the crypt base. g: CryoEM section of crypt stained for GFP with immunogold (scale bar=1000 nm). Quantification of specificity of labeling: Gold particles were counted over 255 μm2 of CBC cell cytosol (1113 particles), 261 μm2 of Paneth cell cytosol (305 particles) and 257 μm2 of fibroblast cytosol (263 particles) outside the crypt. Thus CBC cytoplasm had 4.36 gold particles/μm2 compared to the Paneth cells 1.17 gold particles/μm2 and to the fibroblast control 1.02 gold particles/μm2. C=Crypt lumen; P=Paneth cells; CBC=Crypt Base Columnar cells. h: Unlabeled CryoEM section (scale bar=2000 nm), underscoring the ultrastructural characteristics of CBC cells and their positioning relative to Paneth cells.

FIG. 5. Lineage tracing in the small intestine and colon. a: GPR49-EGFP-Ires-CreERT2 knock-in mouse crossed with Rosa26-LacZ reporter mice 12 hours after Tamoxifen injection b: frequency at which the blue cells appeared at specific positions relative to the crypt bottom, according to the scheme in the inset of FIG. 5b . The large majority of the Cre+ LacZ-labeled CBC cells occurred at positions between the Paneth cells, while only 10% of these cells were observed at the +4 position directly above the cells (blue line). Quantitative data on the position of long term DNA label-retaining cells obtained in adult mice post-irradiation (marking the “+4” intestinal stem cell) were published recently by Potten and colleagues 17. Comparison of these data (red line) with the position of CBC cells carrying activated Cre. c-e: Histological analysis of LacZ activity in small intestine 1 day post-induction (c), 5 days post-induction (d) and 60 days post-induction (e). f-h: Double-labelling of LacZ-stained intestine using PAS demonstrates the presence of Goblet cells (f; white arrows) and Paneth Cells (g; blue arrows) in induced blue clones. Double-labelling with Synaptophysin demonstrates the presence of enteroendocrine cells within the induced blue clones (h; black arrows). i-k Histological analysis of LacZ activity in colon 1 day post-induction (i), 5 days post-induction (j) and 60 days post-induction (k).

FIG. 6. Strategy for EGFP-ires-CreERT2 cassette knock-in into the Gpr49 locus

a: Schematic structure of the mouse Gpr49 gene b: Southern blotting strategy to screen ES cells transfected with a knock-in construct targeting the ATG translational start in Exon I. c: Four ES cell clones out of a total of 500 scored positive for the recombined BamHI band running at 4.3 kb. After re-screening of these 4 ES clones, the first two (asterisks) were selected for blastocyst injections.

FIG. 7. Relative radiation sensitivity of CBC cells, +4 cells, and TA cells. Adult mice were irradiated with 1 Gy or 10 Gy and subsequently sacrificed 6 hours later, at the peak of apoptosis. a: Active Caspase-3-positive cells were visualized by immunohistochemistry (Upper panel—black arrows highlighting positive +4 cells following 1 Gy irradiation; Lower panel—white arrows highlighting positive CBC cells following 10 Gy irradiation). b: The frequency of positive cells per crypt was determined by counting three classes: CBC cells (located between the Paneth cells), +4 cells (located directly above the Paneth cells) and TA cells: located at position 5-15. Maximal apoptosis at +4 is already reached at 1 Gy while 10 Gy causes significantly more apoptosis than 1 Gy irradiation in CBC cells.

FIG. 8. Whole mount analysis of LacZ expression in small intestine of GPR49-EGFP-Ires-CreERT2 knock-in mice crossed with Rosa26-LacZ reporter mice at the indicated time points following Tamoxifen injection a:1 day post-induction. b: 5 days post-induction. c: 60 days post-induction.

FIG. 9. Colocalisation of proliferation marker Ki67 and GFP-positive CBC cells in the intestinal crypts of GPR49-EGFP-CreERT2 mice (serial sections).

FIG. 10. Sequences of the human, mouse and rat receptors.

FIG. 11. Predicted structure of Lgr4, 5 and 6.

FIG. 12. Restricted expression of a GPR49-LacZ reporter gene in adult mice Expression of GPR49lacZ in selected adult mouse tissues. LGR5 is restricted to rare cell populations in the brain (glomeruli of the olfactory bulb and several other poorly defined regions) (A), the eye (inner nuclear layer of the retina) (B), liver (cells surrounding the portal triads) (C) and adrenal gland (D)

FIG. 13. Lineage tracing in the stomach Lgr5-EGFP-CreERT2 mice were crossed with Rosa26R reporter mice and Cre enzyme activity induced in the LGR5+ve cells by IP injection of Tamoxifen. LacZ reporter gene activity is initially restricted to the LGR5 cells (A), but rapidly expands to include the entire epithelium in the Stomach over time (B). This “lineage tracing” is maintained over long periods of time (B). This demonstrates that all epithelial cells are derived from the LGR5+ve population in this tissue, proving that they are stem cells.

FIG. 14. Lineage tracing in the mammary gland Lgr5-EGFP-CreERT2 mice were crossed with Rosa26R reporter mice and Cre enzyme activity induced in the LGR5+ve cells by IP injection of Tamoxifen. LacZ reporter gene activity is initially restricted to the LGR5 cells (A), but expands to include the myoepithelium of newly-formed milk glands in lactating females (B), indicating that LGR5 is specifically marking myoepithelial stem cells in this organ.

FIG. 15. Lineage tracing in the adrenal gland. Lgr5-EGFP-CreERT2 mice were crossed with Rosa26R reporter mice and Cre enzyme activity induced in the LGR5+ve cells by IP injection of Tamoxifen. LacZ reporter gene activity is initially restricted to the LGR5 cells (A), but expands to include the medulla of the adrenal gland (B), indicating that LGR5 is specifically marking adrenal medulla stem cells.

FIG. 16. Lgr6 is expressed in cells of the upper bulge area of the mouse hair follicle and in basal cells of the epidermis. Skin sections of appr. 26 days old Lgr6-EGFP-Ires-CreERT2 mice (early anagen) were obtained and stained for nuclear DNA (Topro) and EGFP visualized using confocal microscopy (A-C). During early anagen Lgr6 is expressed in the upper bulge (A, C) and the basal epidermis (A, B).

FIG. 17. The progeny of Lgr6+ cells contribute to all structures of the hair follicles (HF), interfollicular epidermis (IFE) and sebaceous glands (SG). To trace the progeny of Lgr6+ cells Lgr6-EGFP-Ires-CreERT2/ROSA26-LacZ mice were injected with Tamoxifen™ at P20 when HFs are in telogen (A). At P23 a first staining in the IFE and HFs was detected (B). Analysis of LacZ staining progeny at P38 (1st anagen, C, D) and P52 (2nd telogen, E, F) revealed contribution to all parts of the HFs, IFEs and SGs.

FIG. 18. The progeny of Lgr6+ cells contribute to the myoepithelium of the lung. To trace the progeny of Lgr6+ cells Lgr6-EGFP-Ires-CreERT2/ROSA26-LacZ mice were injected with Tamoxifen™ at P20. Analysis of LacZ staining progeny at P38 (A, 10×, 20× and 40× magnification from left to right) and P52 (B, 10×, 20× and 40× magnification from left to right) revealed contribution to the myoepithelium underlying the bronchioles of the lung.

FIG. 19. Low-dose oral induction with ß-NF does not induce Cre-mediated deletion in stem cells of AHCre mice. Intestinal whole-mounts stained for ß-galactosidase from AhCre+ Rosa26R+ mice. a: No activation of the Rosa-lacZ reporter gene is observed in intestines from non-induced AhCre+ Rosa26R+ mice. b: Readily visible expression of lacZ throughout the intestine 2 days after a single gavage of 1 mg/kg ß-napthoflavone, indicating efficient Cre-mediated activation of the lacZ reporter. No lacZ expression is visible at the crypt base (lower panel) demonstrating the absence of Cre-mediated recombination at the crypt base. c: No lacZ-positive crypt/villus units are visible on whole-mount intestines 100 days post-induction, indicating that this dosing regime very rarely causes recombination within the intestinal stem cells.

FIG. 20. Transformation of non-stem cells through loss of APC does not efficiently drive adenoma formation over extended time-periods. a-c: ß-catenin IHC performed on intestinal sections from AhCre+ Rosa26R+ Apcfl/fl 3 days following a single gavage of 1.0 mg/kg ß-napthoflavone. Clusters of transformed cells with nuclear ß-catenin were frequently observed on the villus (a) and upper regions of the crypt (b). ß-cateninhigh clusters were only very rarely observed at the crypt base (c). These clusters are highlighted with black arrows. d: Quantification of the location of the ß-cateninhigh cell clusters on intestinal sections from AhCre+ Rosa26R+ Apcfl/fl 4 days following a single gavage of 1.0 mg/kg ß-napthoflavone. Box-plots showing numbers of foci observed at the crypt base, the upper crypt and the villus in 1600 crypt-villus units. Significantly more clusters were seen at the upper regions of the crypt than any other region (p=0.04, Mann Whitney, n=3). Nuclear ß-catenin foci were observed only very rarely at the crypt base. e:□-ß-catenin IHC performed on intestinal section from AhCre+ Rosa26R+ Apcfl/fl 24 days following a single gavage of 1.0 mg/kg ß-napthoflavone. Here, nuclear ß-catenin is seen in a small lesion 24 days after cre induction. f,g: ß-catenin IHC performed on intestinal section from AhCre+ Rosa26R+ Apcfl/fl 167 days following a single gavage of 1.0 mg/kg ß-napthoflavone showing a microadenoma (f) and small adenoma (g) with nuclear ß-catenin. h: Quantification of adenoma formation over extended time-periods in AhCre+ Rosa26R+ Apcfl/fl following a single gavage of 1.0 mg/kg ß-napthoflavone. Lesion size was scored on intestinal whole-mounts from AhCre+ Rosa26R+ Apcfl/fl mice that had been stained for lacZ to help visualise the small lesions (at least 3 mice were used for each time-point). No adenomas were seen in mice up to and including day 24 and there was only the very rare microadenoma in mice at day 24. The occasional adenoma was observed in AhCre+ Rosa26R+ Apcfl/fl at 100 days (plus), however the majority of lesion remained microscopic showing that most lesions were not progressing to adenoma despite a long latency period.

FIG. 21. Lgr5+ve intestinal stem cells transformed following loss of APC persist and fuel the rapid formation of ß-cateninhigh microadenomas. a-i: The consequences of Lgr5+ve intestinal stem cell transformation and their subsequent fate was tracked over an eight day period using ß-catenin and GFP as markers of transformed cells and Lgr5+ve stem cells respectively. a-c: Accumulation of the Wnt effector, ß-catenin is first observed in scattered Lgr5+ve stem cells 3 days after Cre induction in Lgr5-EGFP-Ires-CreERT2/APCfl/fl intestines. Representative examples of 1-cateninhigh Lgr5+ve stem cells are circled. d-f: Five days post-induction the transformed Lgr5-GFP+ve stem cells remain (e,f: black arrows) and are associated with clusters of transformed (ß-cateninhigh) cells within the TA compartment. g-h: Eight days post-induction the clusters of transformed cells have expanded to fill the TA compartment (h: red circle). The transformed Lgr5-GFP+ve stem cells at the crypt base persist (h,i: black arrows), but their transformed progeny within the TA compartment are Lgr5-GFP-ve. (h,i: red circles).

FIG. 22. Selective transformation of Lgr5+ve stem cells following loss of APC efficiently drives adenoma formation throughout the small intestine. a-h: The appearance and development of intestinal adenomas and the expression of the Lgr5-GFP stem cell marker within these adenomas was tracked over a 36 day period using GFP (f) and ß-catenin (all others) IHC.a-b: Multiple small adenomas are readily visible throughout the intestine 14 days after Lgr5+ve stem cell transformation. c-f: Multiple macroscopic adenomas (>100) are present after 24 days. Lgr5-GFP expression in adenomas is restricted to rare scattered cells (f; circled). g,h: At 36 days, a large proportion of the intestine is filled with macroscopic adenomas.

FIG. 23. Presence of Lgr5+ stem cells in intestinal adenomas. Intestinal adenomas express high levels of ß-catenin as a result of chronic activation of the Wnt pathway (A). In contrast to other Wnt target genes which are highly expressed throughout the adenoma (not shown), expression of the intestinal stem cell marker Lgr5-GFP is restricted to scattered cells with characteristic stem cell morphology: slender, comma-shaped cells; indicated with black arrow (B). We speculate that these Lgr5+ve cells within the adenoma are stem cells dedicated to maintaining the growth of the adenoma (so-called cancer stem cells).

FIG. 24. FACS analyses of LGR5 expression in L8 cells, which are clonal derivatives of LS174T cells, which express dominant negative Tcf4 (DNTcf4) upon Doxycycline (DOX). DNTcf4 turns off constitutive active Wnt pathway. After 48 hrs of DOX induction, a reduction in hLgr5 protein levels is observed. Rat IgG is used as negative isotype control. 9G5 is a rat monoclonal derived antibody directed against hLgr5

FIG. 25. Comparison of Lgr5+ stem cells and their direct progeny. GFP-positive epithelial cells from cell suspensions prepared from freshly isolated crypts of Lgr5-EGFP-ires-CreERT2 mice. FACS analysis distinguished a GFP-high (GFPhi) and a GFP-low (GFPlo) population, which we tentatively identified as CBC cells and their immediate transit-amplifying daughters, respectively (A). An example of a Wnt-responsive gene, Sox9, which shows high level expression in CBC cells, but TA cells directly above the Paneth cells also express this gene in in situ hybridizations, albeit at a much lower level (B).

FIG. 26. Endogenous hLgr5 staining of a human colon cancer cell line (L8) using several Lgr5-specific monoclonal antibodies. L8 cells are a clonal derivative of the parental LS174T cell-line. Following Doxycycline (DOX) induction the L8 cells express a dominant-negative form of Tcf-4 (DNTcf4). DNTcf4 efficiently blocks the constitutive Wnt pathway activity in these cells and consequently switches off Tcf target genes. After 48 hrs of DOX induction a major reduction in hLgr5 protein levels is observed. Rat IgG is used as negative isotype control.

FIG. 27. Light chain+heavy chain sequences analyzed using KABAT method. CDR regions are in bold and in italics.

EXAMPLES Example 1 Experimental Part

Northern Blotting and Induced Wnt Pathway Inhibition in LS174T Clone L8:

As in van de Wetering, M. et al. The beta-catenin/TCF-4 complex imposes a crypt progenitor phenotype on colorectal cancer cells. Cell 111, 241-50 (2002). The probe spanned the entire reading frame of mouse Gpr49. Crypt and villus epithelial preparations for RNA isolation were generated from 0.5 cm lengths of intestine by 4 successive rounds of incubation in pre-warmed 30 mM EDTA at 37° C. for 10 minutes, followed by vigorous shaking (10×) in ice-cold PBS. Fractions 1 and 4, comprising predominantly villi and crypts respectively were used for RNA isolation.

Mice:

GPR49-LacZ mice were generated by homologous recombination in ES cells targeting an Ires-LacZ cassette to the 5′ end of the last exon, essentially removing the region containing all TM regions and creating a null allele (Lexicon). GPR49-EGFP-Ires-CreERT2 mice were generated by homologous recombination in ES cells targeting an EGFP-Ires-CreERT2 cassette to the ATG of GPR49. Rosa26-lacZ Cre reporter mice were obtained from Jackson Labs.

Tamoxifen Induction:

Mice of at least 8 weeks of age were injected once intraperitoneally with 200 μl of Tamoxifen in sunflower oil at 10 mg/ml.

Brdu Injection:

Mice were injected intraperitoneally at four hour intervals with 200 μl of a BrdU solution in PBS at 5 mg/ml.

Immuno Electron Microscopy:

Intestines were dissected and perfuse-fixed in 4% PFA in 0.2 M PHEM-buffer, embedded in gelatine, cryosectioned with a Leica FCS cryoultratome and immunolabelled against GFP with polyclonal rabbit anti-GFP antibody. Samples were trimmed using a diamond Cryotrim 90 knife at −100° C. (Diatome, Switzerland) and ultrathin sections of 70 nm were cut at −120° C. using a Cryoimmuno knife (Diatome, Switzerland). For the low magnification EM images the 15 nm protein A-gold particles (UMCU, Utrecht, The Netherlands) were briefly silver enhanced with R-GENT SE-EM (Aurion, The Netherlands) according to the manufacturers instructions. Aspecific binding to Paneth cell granules was diminished by applying Blocking solution (Aurion, The Netherlands) prior to the primary antibody.

Tissue Sample Preparation for Immunohistochemistry, In-Situ Hybridization and LacZ Expression Analysis:

All performed as previously described in Muncan, V. et al. Rapid loss of intestinal crypts upon conditional deletion of the Wnt/Tcf-4 target gene c-Myc. Mol Cell Biol 26, 8418-26 (2006). In-situ probes comprising a 1 kb N-terminal fragment of mGPR49 were generated from sequence-verified Image Clone 30873333. Ki67 antibodies were purchased from Monosan (The Netherlands), Phospho-histone H3 from Campro Scientific (The Netherlands), anti-synaptophysin from Dako, anti BrdU from Roche. Polyclonal rabbit anti-GFP was provided by Edwin Cuppen, Hubrecht Institute.

Generation of Suspension of Human (Tumor) Tissue Cells.

Using a razor blade, mince freshly isolated human (tumor) tissue as much as possible. Do this in serum-free media. Draw minced tumor into a 25 ml pipette. Place the solution into a 50 ml conical tube. Incubate at 37 C for 30-60 min after adding collagenase IV (200 units/ml) (Sigma). The final concentration should be 200 units/ml. Pipette up and down a few times every 10 min (approx). Pass the solution through a filter (45 micrometer pore size; Becton Dickinson). Wash the filter with 4-5 ml of serum-free medium. Centrifuge the solution @1500 rpm for 10 min (4° C.) Resuspend the pellet in hypotonic ammonium chloride (approx. 5 ml). Leave 10 min at room temperature (this will lyse red blood cells). Then add equal volume of serum-free media and centrifuge again. Resuspend pellet in serum free medium. If clumpy then pass through another filter. Count with trypan blue to see the percent dead cells.

Cancer Stem Cell Assay by Xenografting in Immunodeficient Mice

The mice are sublethally irradiated with 320 Rad. The experimental procedure involves injecting human (colon) cancer cell suspensions under the renal capsule of NOD/SCID mice. The mice are handled using sterile techniques and anaesthetized using inhalational anaesthesia: isoflurane. The mice are placed on a heating pad during the procedure.

A clipper is used to shave the abdomen, which is then prepped sequentially with: (1) iodine based solution and (2) 70% ethanol solution. The area is then dabbed with a gauze. The mouse is placed on its side (left side up). A 1 cm (approximately) flank incision is made with scissors, just below the costal margin on the left side. Deliver the kidney into the wound. The cell suspension to be assayed for cancer stem cell activity is mixed 1:1 (medium: Matrigel) on ice. Utilizing a tuberculin syringe, inject 25 microliter of the cell suspension under the renal capsule. Deliver the kidney back into the abdomen. If cancer stem cell activity is present in the cell suspension, a tumor will grow out in the subsequent weeks/months which is analysed by histology and should resemble the original human tumor.

The intestinal epithelium is the most rapidly self-renewing tissue in adult mammals. Current models state that 4-6 crypt stem cells reside at the +4 position immediately above the Paneth cells in the small intestine; colon stem cells remain undefined. Gpr49/Lgr5 was selected from a panel of intestinal Wnt target genes for its restricted crypt expression. Two knock-in alleles revealed exclusive expression of Gpr49 in cycling, columnar cells at the crypt base. In addition, Gpr49 was expressed in rare cells in several other tissues including stomach, breast and hair follicle. Using an inducible Cre knock-in allele and the Rosa26-LacZ reporter strain, lineage tracing experiments were performed in adult mice. The Gpr49^(+ve) crypt base columnar cell (CBC) generated all epithelial lineages over a 60-day period, implying that it represents the stem cell of the small intestine and colon. The expression pattern of Gpr49 shows that it marks stem cells in multiple adult tissues and cancers.

The absorptive epithelium of the small intestine is ordered into crypts and villi¹ (References 2). In the mouse, the small intestinal epithelium turns over every 3-5 days. The massive rate of cell production in the crypts is balanced by apoptosis at the tips of the villi. To date, intestinal stem cells have not been functionally identified, due to the lack of unique markers and the absence of stem cell assays. The analysis of mouse chimeras and mutagen-induced somatic clones^(2, 3) (References 2) and the study of regeneration upon injury have allowed an operational definition of stem cell characteristics. Stem cells are believed to cycle steadily to produce the rapidly proliferating transit amplifying (TA) cells capable of differentiating towards all lineages. Stem cells self-renew throughout life, and regenerate the epithelium following injury. The estimated number of stem cells is between 4 and 6 per crypt² (References 2). Long-term DNA label retention has tentatively located stem cells at “position +4” directly above the Paneth cells⁴ (References 2). Three differentiated cell types (enterocytes, goblet cells and enteroendocrine cells) form from TA cells at the crypt-villus junction and continue their migration in coherent bands stretching along the crypt-villus axis. While crypts are monoclonal, each villus receives cells from multiple different crypts and is therefore polyclonal. The fourth major differentiated cell-type, the Paneth cell, resides at the crypt bottom. The colon epithelium contains crypts, but has a flat surface rather than carrying villi. This epithelium comprises two major differentiated cell types: the absorptive colonocytes and the goblet cells' (References 2). To date, no stem cells have been identified in the colon.

Since Wnt signals constitute the major driving force behind the biology of the crypt⁵ (References 2), we hypothesized that one or more Wnt/Tcf4(Tcf7l2) target genes may be specifically expressed in the stem cells. We have previously described the Wnt/Tcf4 target gene program in colorectal cancer cells and found that it is physiologically expressed in intestinal crypts^(6, 7) (References 2). When we studied the expression of approximately 80 selected Tcf4 target genes⁷, the overwhelming majority was expressed either in Paneth cells or TA cells. The Gpr49/Lgr5 gene, however, was expressed in a unique fashion. The Gpr49 gene behaved as a Wnt target gene, as its expression was extinguished upon the induced inhibition of Wnt pathway activity by dominant-negative TCF4 in the human colorectal cancer cell line LS174T, a cell system described earlier⁶ (References 2) (FIG. 1a , lane 1 vs. 2). Accordingly, the gene was expressed in the crypts, but not the villi, of mouse small intestine (FIG. 1a , lane 3 vs. 4). In situ hybridization revealed expression in a limited number of cells located at all crypt bottoms as well as in adenomas in the small intestine of an APC^(min) mouse (FIGS. 1b and c ). This expression pattern, enlarged in FIG. 2c , clearly differed from that obtained with a Paneth cell-specific gene (FIG. 2a ) or a TA-specific gene (FIG. 2b ). The Gpr49 gene appeared to mark small cells interspersed between Paneth cells, the cycling Crypt Base Columnar (CBC) cells (FIG. 2d-h ; see below).

Gpr49 encodes an orphan G protein-coupled receptor (GPCR), characterized by a large leucine-rich extracellular domain. It is closely related to GPCRs with glycoprotein ligands, such as the TSH-, FSH- and LH-receptors⁸ (References 2). Gpr49 was on our original list of Tcf4 targets in colorectal cancer⁶, but has since been observed to be overexpressed also in ovarian and hepatocellular carcinomas^(9, 10) (References 2). In order to study its expression in detail we obtained a knock-in allele, in which LacZ, preceded by an internal ribosome entry site (ires), is integrated just N-terminal to the first transmembrane domain essentially creating a null allele (FIG. 3a ).

While our study was in progress, Morita et al published the Gpr49^(−/−) phenotype¹¹ (References 2). A malformation of the tongue and lower jaw causes newborn mutants to swallow large amounts of air leading to their demise soon after birth. We observed the same phenotype in our mice. Of note, crypts and intestinal stem cells are first established several weeks after birth¹² (References 2). The heterozygous Gpr49-LacZ mice allowed us to detail the expression of Gpr49. Before birth, a dynamic and complex expression pattern was observed (Barker et al, in preparation). Around birth, Gpr49 expression subsided in virtually all tissues. Expression in adult mice was restricted to rare, scattered cells in the eye, brain, hair follicle, mammary gland, reproductive organs, stomach and intestinal tract (FIG. 3, and not shown). In the small intestine, Gpr49 expression was observed in slender cells located between the Paneth cells in the small intestine (FIGS. 3b and c ) and in a similar number of cells at the bottom of colon crypts (FIGS. 3d and e ). Counting of blue cells in small intestinal crypts sectioned through the lumen revealed the presence of approximately 3.5 of such cells per sectioned crypt (FIG. 2i , white bar). More than 30 years ago, Leblond and Cheng noted the presence of cycling cells between the Paneth cells and have coined the term “Crypt Base Columnar” (CBC) cells 13 (References 2). Based on their position and their presence in long-term mutant epithelial clones, Cheng and Bjerknes^(2, 14) (References 2) and Gordon and colleagues¹⁵ (References 2) have proposed that these cells may harbor stem cell activity

By morphology, the slender Gpr49^(+ve) CBC cells with their scant cytoplasm and flat, wedge-shaped nuclei pointing towards the crypt lumen were readily distinguishable from the adjacent Paneth cells. Occasionally (once in approximately every ten crypts), these cells also expressed the M phase marker phospho-histone H3, indicating that the cells are in cycle (FIG. 2f ). Indeed, a 4 hour pulse of BrdU labeled approximately 1 of these cells per crypt (FIGS. 2G and 2I, left black bar), while a 24 hour continuous BrdU labeling resulted in more than 3 positive cells per crypt (FIGS. 2h and i , right black bar), close to the total number of CBC cells per crypt (FIG. 2i , white bar). This observation implied that the average cycling time of CBC cells is in the order of 1 day. Direct colocalization of the proliferation marker Ki67 with GPR49-LacZ further confirmed that the LacZ positive CBC cells are typically cycling (FIG. 2e and FIG. 9).

In order to be able to visualize live CBC cells and to study their potential “stemness”, we generated another knock-in allele, in which we integrated an EGFP-ires-CreERT2 cassette at the first ATG codon of Gpr49 (FIG. 4a and FIG. 6). Heterozygous mice carrying this allele were healthy and fertile. The GFP pattern observed in adult tissues faithfully recapitulated the pattern previously seen with the Gpr49-LacZ allele in eye, brain, hair follicle, mammary gland, reproductive organs, stomach and intestinal tract (not shown, and FIG. 4). Confocal imaging allowed the visualization of the Gpr49^(+ve) cells by GFP fluorescence in small intestine (FIG. 4 b,c,e) and colon (FIG. 4f ). Immuno-Electron Microscopy using immunogold labeling of the GFP-positive CBC cells and of neighbouring Paneth cells and fibroblasts illustrated the unique ultrastructural anatomy of the CBC cells (FIGS. 4g and h ). Typically, the CBC cells were relatively broad at their base, contained a flat wedge-shaped nucleus and scarce organelles. A slender extension of apical cytoplasm was squeezed inbetween neighboring endoplasmic reticulum- and granule-rich Paneth cells, extended to the crypt lumen and carried some apical microvilli.

We then crossed the EGFP-ires-CreERT2 knock-in allele with the Cre-activatable Rosa26-LacZ reporter¹⁶ (See FIG. 4a for experimental strategy). Injection of Tamoxifen activates the CreERT2 fusion enzyme in Gpr49-expressing cells. Cre-mediated excision of the roadblock sequence in the Rosa26-LacZ reporter should then irreversibly mark the Gpr49^(+ve) cells. Moreover, while potential progeny of these cells will no longer express GFP, the activated LacZ reporter should act as a genetic mark, facilitating lineage tracing.

LacZ expression was not observed in non-induced mice (not shown). To quantify the total number of CBC cells per crypt in which the latent Cre enzyme could be activated by Tamoxifen, we treated 2-3 months-old mice with Tamoxifen and sacrificed the mice 12 hours later. As evident in FIG. 5a , blue LacZ signals appeared at the typical CBC positions. We determined the frequency at which the blue cells appeared at specific positions relative to the crypt bottom, according to the scheme in FIG. 5b . The large majority of the Cre^(+ve), LacZ-labelled CBC cells occurred at positions between the Paneth cells, while only 10% of these cells were observed at the +4 position directly above the cells (FIG. 5b , blue line). Quantitative data on the position of long term DNA label-retaining cells obtained in adult mice post-irradiation (marking the “+4” intestinal stem cell) were published recently by Potten and colleagues¹⁷. Comparison of these data (FIG. 5b , red line) with the position of CBC cells with activatable Cre revealed that the two markers identified largely non-overlapping cell populations.

Another defining characteristic of the +4 cell is their exquisite sensitivity to low dose (<1 Gy) radiation⁴. To compare relative radiation sensitivity between CBC cells and +4 cells, adult mice were irradiated with 1 Gy or 10 Gy and subsequently sacrificed 6 hours later, at the peak of apoptosis. Active Caspase-3-positive cells were visualized by immunohistochemistry (FIG. 7a ). The frequency of positive cells per crypt was determined by counting apoptotic cells in three classes: CBC cells (defined by their location between the Paneth cells), +4 cells (located directly above the Paneth cells) and TA cells: located at position 5-15 (FIG. 7b ). Maximal apoptosis at the +4 position was already reached at 1 Gy (a: upper panel, black arrows) in concordance with⁴ (References 2), while 10 Gy caused significantly more apoptosis than 1 Gy irradiation in CBC (a: lower panel) and TA cells, confirming the different identities of the CBC and +4 cells.

Adult mice were then subjected to a Tamoxifen pulse and were sacrificed at 1, 5, 12 (not shown) and 60 days post-induction. One day post-induction, occasional CBC cells in the crypts of small intestine and colon were observed to express LacZ (FIGS. 5c and 5i respectively). As is demonstrated for whole-mount small intestine in FIG. 8, parallel ribbons of cells emanated from the crypt bottoms and ran up the side of adjacent villi at later time points. The kinetics of stripe formation was not uniform. Some stripes already reached the villus tips 5 days post-induction, while blue staining in occasional crypts was still restricted to crypts. At 5 days post-induction (FIG. 5d ), such crypt-restricted expression was very rarely seen. The CBC cells were capable of long-term maintenance of the self-renewing epithelium, since in 60-day intestines (FIG. 5e and FIG. 8) the frequency of blue crypts and ribbons was essentially identical to that seen at 5-12 days post-induction.

Double-labeling of 60 day-induced intestine demonstrated the presence of PAS-positive goblet cells (FIG. 5f ), PAS-positive Paneth cells (FIG. 5g ) and synaptophysin-positive enteroendocrine cells (FIG. 5h ) in the LacZ-stained clones originating from the GPR49^(+ve) CBC cells. Using mutational marking, Cheng and Bjerknes have reported the existence of different types of long-lived epithelial clones, i.e. columnar (enterocyte) clones, mucous (goblet) clones and mixed clones². The clones observed in our study were exclusively of the mixed variety. In blue clones, the frequency of goblet cells (114 out of 2043 total cells counted), enterocytes (1846/2043) and Paneth cells (83/2043) was comparable to the frequency of goblet cells (127 out of 3691 total cells counted), enterocytes (3345/3691) and Paneth cells (127/3691) in unmarked adjacent epithelium. As noted² (References 2), the third secretory cell type, the enteroendocrine cell, was too rare to allow accurate enumeration. Taken together, we conclude that the Gpr49^(+ve) CBC cells represent the genuine stem cells of the small intestine.

Analysis of the colon yielded essentially identical observations. The Gpr49^(+ve) cells yielded blue clones emanating from the crypt bottom (FIG. 5i ). These clones contained colonocytes as well as goblet cells, and essentially remained unchanged during the 60 days of chase (FIG. 5j,k ). One significant difference with the situation in the small intestine involved the kinetics of clone-formation. At 5 days, blue staining in most crypts was still restricted to the bottom and entirely blue crypts were only rarely observed, implying that the colon stem cells were more often quiescent than their small intestinal counterparts. At later days, the relative number of entirely blue crypts increased. We concluded that the Gpr49^(+ve) colon cells fulfilled the stem cell requirements in being pluripotent and capable of maintaining epithelial self-renewal over long periods of time.

Our observations provide the definitive characterization of the intestinal stem cell by lineage tracing using the expression of a single marker gene, Gpr49. The small intestinal Gpr49^(+ve) cells are generally not quiescent, but are rapidly cycling, as evidenced by the expression of Ki67 and phospho-histone H3, the incorporation of BrdU, and by the kinetics of ribbon formation. Gpr49^(+ve) cells of the small intestine appear more actively dividing than their colonic counterparts, likely reflecting differences in the rate of epithelial turnover between the two organs. It appears somewhat counterintuitive that stem cells cycle. This is, however, not unprecedented. Germ stem cells in the Drosophila testis and ovary of the fly, arguably the best understood adult stem cells in animals, cycle throughout the lifetime of the adult fly¹⁸ (References 2). Similarly, a recent elegant study demonstrated that adult stem cells of mammalian skin are continuously cycling¹⁹ (References 2).

The cycling +4 cells have previously been proposed by Potten and colleagues to represent the small intestinal stem cells⁴ (References 2), a notion not confirmed here. The notion was based on the observation that a DNA label incorporated during periods of high stem cell activity was specifically retained in cells at the +4 position. Long-term label retention is often used as an indirect strategy to identify stem cells¹² (References 2). It should be noted, however, that terminally differentiating cells will also retain DNA labels and that label retention should therefore be interpreted with caution. Previous studies have proposed other markers for intestinal stem cells. Musashi^(20, 21) (References 2) and CD133²² (References 2) in our hands stain up to 30-50 cells per crypt (not shown), which appear to encompass CBC cells as well as early transit amplifying cells. Li and colleagues have described several molecular markers for the +4 cells, including phospho-PTEN, phospho-AKT and 14-3-3ζ²³ (References 2). Our current study implies that the validity of these putative stem cell markers should be reconsidered.

It appears rather unique that adult stem cells can be identified based on the expression of a single gene. This phenomenon may not be restricted to the intestine, since we observe highly restricted Gpr49 expression in a variety of other tissues. In the anagen hair follicle, the Gpr49 gene is expressed in the bulge area as well as in the outer root sheath (FIG. 3i ). While quiescent LTR stem cells reside exclusively in the bulge, activated stem cells migrate down through the outer root sheath towards the basal papilla²⁴⁻²⁶ (References 2). Indeed, Gpr49 was recently reported to be the second most highly upregulated gene as assessed by differential expression arraying on isolated hair follicle stem cells²⁷ (References 2). Moreover, preliminary lineage tracing experiments in the hair follicle support the notion that Gpr49^(+ve) cells represent stem cells (Barker, Clevers and Toftgard, unpublished). While patterns of proliferation in stomach glands have indicated that the epithelial stem cells reside at the isthmus, halfway between the gland base and epithelial surface²⁸ (References 2) we find Gpr49 expressed at gland bottoms (FIG. 3f,g ). Ongoing lineage tracing experiments imply that the entire glands derive from these cells (Barker and Clevers, unpublished). In the mammary gland, stem cells reside in the basal epithelial layer²⁹ (References 2), where we observe Gpr49 expression (FIG. 3h ). Gpr49 may thus represent a more general marker of adult stem cells. If true, the mouse models developed in the course of this study will allow the isolation as well as specific genetic modification of live adult stem cells in a variety of organs. We first identified Gpr49 as a gene expressed in colon cancer cells⁶ (References 2). It is expressed in other cancers^(9, 10) (References 2) and, as described in the current study, also in premalignant mouse adenomas. Based on the observations reported here, we now know that Gpr49 may mark cancer stem cells (“tumor-initiating cells”) in colorectal adenocarcinomas.

Example 2 Lgr5 Tissue Expression and Evidence for Lgr5⁺ Stem Cells in these Tissues Materials and Methods

For experimental details, we refer to materials and methods as used in example 1

Results and Discussion Lgr5 Expression Also Detected in Brain, Retina, Liver and Adrenal Gland

We studied the Lgr5 expression in multiple other tissues in the mice carrying lacZ integrated into the last exon of the Gpr49 gene, removing all transmembrane regions of the encoded Gpr49 protein. We determined that, analogous to colon and small intestine, Lgr5⁺ cells were detected in brain, retina, liver and adrenal gland (FIG. 12). In adult mice, LGR5 is restricted to rare cell populations in the brain (glomeruli of the olfactory bulb and several other poorly defined regions), the eye (inner nuclear layer of the retina), liver (cells surrounding the portal triads) and adrenal gland.

Lineage Tracing in the Stomach, Mammary Gland and Adrenal Gland Proves that Lgr5 is Marking Stem Cell Populations in these Tissues

We used the LGR5KI/Rosa26-lacZ mice¹⁶ (See example 1 for experimental strategy) to study the presence of Lgr5⁺ stem cells in multiple other tissues. Injection of Tamoxifen activates the CreERT2 fusion enzyme in Gpr49-expressing cells. Cre-mediated excision of the roadblock sequence in the Rosa26-LacZ reporter should then irreversibly mark the Gpr49^(+ve) cells. Moreover, while potential progeny of these cells will no longer express GFP, the activated LacZ reporter should act as a permanent genetic mark, which will be passed on to any descendents of the LGR5+ve cells, allowing us to track their appearance and fate in-vivo.

Lineage tracing was initiated in young LGR5KI/Rosa26-lacZ mice and the stomach epithelium analyzed for LacZ activity after 6 months. LGR5-lacZ positive cells are initially restricted to the base of the glands (FIG. 13a ). After 6 months, multiple entirely lacZ-positive glands are visible throughout the stomach (FIG. 13b ), demonstrating that the LGR5+ve cells are capable of generating all cell-types on the glandular epithelium over long periods of time.

Similar lineage tracing experiments were performed and the mammary gland epithelium analyzed for LacZ activity over a 3 month period. LGR5-lacZ positive cells are initially restricted to rare basal epithelial cells on virgin glands (FIG. 14a ). Following pregnancy, LacZ-positive cells are visible in the basal epithelium of the newly-formed milk glands (FIG. 14b ). This demonstrates that LGR5⁺ cells in the mammary gland are myoepithelial stem cells.

Lineage tracing in the adrenal glands analyzed for LacZ activity over a 3 month period. LGR5-lacZ positive cells are initially restricted to the periphery of the adrenal gland 5 days after induction (FIG. 15a ). After 3 months the majority of the adrenal medulla is LacZ positive (FIG. 15b ). This remains positive over a 14 month period (not shown). This demonstrates that the LGR5⁺ cells are the stem cells of the adrenal medulla.

Example 3 Lgr6 Tissue Expression and Lgr6 Expression in Related Stem Cells Material and Methods Transgenic Mice and Treatments.

Lgr6-EGFP-Ires-CreERT2 mice were generated by homologous recombination in embryonic stem cells targeting an EGFP-Ires-CreERT2 cassette to the ATG of Lgr6. Rosa26-LacZ reporter mice were obtained from the Jackson laboratory. Mice were fed ad libitum. The Cre recombinase was activated in Lgr6-EGFP-Ires-CreERT2/Rosa26-LacZ mice by injecting 200 μl of tamoxifen (10 mg/ml dissolved in sunflower oil) intraperitoneally.

Confocal Analysis of EGFP Expression

For confocal imaging the skin samples were fixed in formalin for 15 minutes at RT and embedded in 4% low melting agarose. Longitudinal sections between 100 and 200 μm thick were prepared using a vibratome. Sections were then permeabilized in PBS supplemented with 1% BSA+1% DMSO+0.1% TritonX, stained for 30 minutes with TO-PRO 1:1000 dilution (Molecular Probes) and embedded using Vectashield (Vector Labs). Sections were imaged with a Sp2 confocal microscope (Leica) and processed using Volocity and Photoshop CS2 software.

Detection of Beta-Galactosidase Activity

Freshly obtained tissues were fixed for 2 hours in 1% Formaldehyde/0.2% glutaraldehyde/0.02% NP40 in PBS0 solution at 4° C. on a rolling platform. Samples were washed 3 times for 20 min with rinse buffer (2 mM MgCl₂/0.02% NP40/PBS0) and stained for 36-48 h in a solution consisting of 1 mg/ml X-gal, 5 mM ferrothiocyanide, 5 mM ferrithiocyanide, 0.1% sodium deoxycholate in rinse buffer. The substrate was removed and the samples washed twice in PBS0 for 20 min at room temperature on a rolling platform. The tissues were then fixed overnight in 4% PFA in PBS0 at 4° C. in the dark on a rolling platform. The PFA was removed and the tissues washed twice in PBS0 for 20 min at room temperature. The samples were embedded in paraffin, sectioned (4 μm) and counterstained with neutral red.

Results and Discussion

To characterize the expression of Lgr6 in the skin we utilized a knock-in mouse, where the Lgr6 promoter controls the expression of EGFP and the CreERT2 fusion protein, termed Lgr6-EGFP-Ires-CreERT2. At P25 when the hair follicles (HFs) are in the growing (anagen) phase, the GFP-positive cells were localized to cells of the upper bulge/isthmus area of the HF (FIG. 16A, C) and basal cells of the interfollicular epidermis (IFE, FIG. 16A, B). This expression pattern suggests that Lgr6 expression marks a SC/early progenitor cell population of the hair follicle and the epidermis.

To address the question whether the Lgr6⁺ cells of the anagen HF and IFE represent functional stem cells 20 day-old Lgr6-EGFP-Ires-CreERT2/Rosa26-LacZ mice were injected with tamoxifen. At P20 Lgr6 is expressed in the upper bulge/isthmus area of the HF and basal cells of the IFE (data not shown). Three days post tamoxifen injection a scattered pattern of labeled cells could be seen in the HFs and the IFE (FIG. 17B). At 18 days post-injection the progeny of Lgr6⁺ cells could be seen in the anagen HFs (FIG. 17C, D) as well as in the IFE and the sebaceous glands (SG) (FIG. 17C, D). In the next telogen labeled cells were found in the bulge and isthmus of the HFs (FIG. 17E, F) and the IFE and SGs (FIG. 17E, F). This observation strongly suggests that Lgr6⁺ cells located in the bulge/isthmus area of the HF and the basal IFE exhibit stem cell properties. In particular, Lgr6⁺ cells can contribute to all the appendages of the skin, i.e. the growing HFs, the IFE and the SG.

It seems rather unique that adult stem cells can be identified on the basis of expression of a single gene, in this case Lgr6. This phenomenon may not be restricted to the skin, because we observe highly restricted expression of Lgr6 in a variety of other tissues. To address the question whether the Lgr6+ cells represent functional stem cells in any other tissues 20 day-old Lgr6-EGFP-Ires-CreERT2/Rosa26-LacZ mice were injected with tamoxifen. LacZ staining was performed on 18 and 32 days post tamoxifen injection to assess for lineage tracing in a variety of tissues. Interestingly, LacZ positive cells were present in the myoepithelium underlying the bronchioles of the lung at both timepoints (FIG. 18). Thus, Lgr6+ cells contribute to the myoepithelium of the lung strongly suggesting that Lgr6⁺ cells located in the lung exhibit stem cell properties as well.

Example 4 The Role of Lgr5⁺ Cancer Stem Cells in Adenoma

The anatomy of the intestinal crypt is uniquely suited to study adult stem cells in their niche. The epithelium of the murine small intestine renews every five days^(1, 2) (references 5). Vigorous proliferation occurs within the crypt compartment. We have recently identified slender, undifferentiated cells expressing the Lgr5 gene located at crypt bottoms as the stem cells of the small intestine and colon. Each small intestinal crypt contains approximately 6 independent, long-lived stem cells that are intermingled with Paneth cells in the small intestine and with goblet cells in the colon. Counter-intuitively, these cells are not quiescent, but complete a cell cycle every day³ (references 5). Leblond and colleagues have originally named these cells morphologically Crypt Base Columnar (CBC) cells^(4, 5) (references 5). Their daughter cells constitute the readily distinguishable transit amplifying (TA) crypt compartment. TA cells divide every 12-16 hours, generating some 300 cells per crypt every day⁶ (references 5). Newly-formed TA cells reside within crypts for approximately 48-72 hours, undergoing up to 6 rounds of cell division while migrating upwards⁶ (references 5). When the committed TA cells reach the crypt-villus junction, they rapidly and irreversibly differentiate. The proliferation is balanced by apoptosis at the other end of the epithelial conveyor belt, the tip of the villus. Only Paneth cells escape this flow; they have a residence time of 3-6 weeks at the crypt base⁷⁻⁹ (references 5). Initiating mutation in intestinal malignancies in mouse and man target components of the Wnt pathway, most frequently the negative Wnt regulator APC^(10, 11) (references 5). This results in the constitutive activation of a Wnt target gene program that drives the formation of benign adenomas or polyps¹²⁻¹⁵ (references 5). However, it remains unclear which cell type sustains the cancer-initiating mutation.

The Cytochrome P450-promoter-driven AH-Cre mouse allows conditional deletion of floxed alleles in the intestinal epithelium following administration of the inducing agent, ß-Napthoflavone (ß-NF). Importantly, the AH-Cre allele is highly active in all cell types of the epithelium, including the stem cells¹⁶ (references 5). We have previously employed a floxed allele of APC¹⁷ (references 5) in combination with the AH-Cre mouse line to demonstrate that acute loss of APC throughout the adult intestinal epithelium following IP injection of ß-NF leads to an immediate quantitative transformation of the epithelium¹⁶ (references 5), a process almost entirely dependent on the downstream Wnt target gene c-Myc¹⁸ (references 5). High-dose oral ß-NF induces more stochastic deletion of APC, resulting in rapid adenoma formation throughout the intestine within 3 weeks¹⁹ (references 5). Both these high-dose induction protocols effect deletion in all compartments of the epithelium, including the stem cells at the crypt base.

Having validated the AHCre/APC^(flox/flox) mouse as an inducible model of intestinal cancer, we sought to dissect the mechanism of adenoma formation by identifying its cell-of-origin. We reasoned that oral administration of low-dose ß-NF would restrict its range of action to cells on the villi and the upper regions of the crypts. Careful titration of the required dosage revealed that following oral administration of 1 mg/kg ß-NF, the efficiency of Cre activation in the stem cells at the crypt base was extremely low, as measured by the negligible frequency of long-term lineage tracing initiated in AHCre/R26R mice receiving this dose. This dose was still very efficient in inducing Cre activity in the TA compartment and villus epithelium, as detected using the Rosa26-LacZ mouse²⁰ (references 5) as a Cre reporter (FIG. 19a, b ). In a typical experiment over 70% of villi contained blue cells 2 days after induction, but at day 7 blue staining could no longer be detected. In line with this, no crypt/villus ribbons were detected at day 100 post-oral induction (FIG. 19c ).

Using this dosing regime on AHCre/APC^(flox/flox)/R26R mice, multiple ß-cateninhigh foci/lesions rapidly became visible throughout the upper crypt and villus epithelium. Representative pictures taken at day 3 post-induction are given in FIG. 20. Mutant APC foci evident by high ß-catenin levels occurred predominantly at crypt-villus junctions, but were also seen on the villi (FIG. 19d ). Very infrequently these lesions were also seen near the crypt base.

The majority of the APC-deficient cells present on the villus epithelium were lost after 4-5 days, presumably by shedding. The remaining APC-deficient lacZ-positive lesions/foci present within the crypts failed to expand over a 24 day period. A typical example of such a lesion is given in FIG. 20e . No macroscopic adenomas were visible at this stage. Strikingly, these small lesions persisted over a 180 day period (FIG. 20g ), and only very rarely progressed to small adenomas, which did not expand beyond 2-3 villi (FIG. 20f, h ). This was in stark contrast to the high frequency formation of large adenomas initiated in the AHcre/APC^(flox/flox) mice following high-dose ß-NF induction. This suggested that the vast majority of adenomas in the latter mice resulted from loss of APC in stem cells.

In order to formally prove that transformation of intestinal stem cells is the major route to adenoma formation, we employed our Lgr5-EGFP-ires-CreERT2 knock-in mice as a stem cell-specific Cre line to inducibly delete the floxed APC. To this end, Lgr5-EGFP-ires-CreERT2×APC^(flox/flox) mice were generated. In these mice, the stem cell-specific Cre enzyme was activated with a single IP injection of Tamoxifen (FIG. 21a ). Subsequent phenotypic changes in the intestine were tracked over a 2 month period. Accumulation of the Wnt-effector protein ß-catenin was first observed in isolated CBC cells at the crypt base after 3 days (FIG. 21a ). These transformed cells were GFP-positive, confirming the targeted deletion of APC in the intestinal stem cells (FIG. 21b ). After 5 days, multiple crypts throughout the intestine were observed to harbor transformed (i.e. ß-catenin^(high)) stem cells in association with highly proliferative clusters/pockets of ß-catenin^(high) cells within the transit-amplifying (TA) compartment (FIG. 21c, d ). This indicated that the Wnt-transformed stem cells remain viable and rapidly generate an expanding population of transformed progeny higher up the crypts. Eight days after inducing APC deletion in the stem cells, the “pockets” of transformed cells had continued to expand within the crypts and outpockets/evaginations of the crypt epithelium and small microadenomas within the associated villus stroma became evident (FIG. 21e ). Cells with accumulated ß-catenin were never present on the villus epithelium in these mice, demonstrating that the expanding transformed population were restricted to the intestinal crypts. These observations are strikingly reminiscent of a model of adenoma formation, in which Wnt-transformed cells expressing high levels of the Wnt target gene EphB2 and -B3 expand within the crypt until they come into contact with the Ephrin-positive villus epithelium^(21,22) (references 5). The resulting repulsive forces consequently dictate that the microadenoma can only continue to expand by invading the stroma of the neighbouring villus where it is shielded from the Ephrin-positive villus epithelium.

The “outpockets” and microadenomas present in the 8 day induced Lgr5KI/APC^(flox/flox) mice continued their aggressive expansion, as evidenced by the presence of multiple large adenomas throughout the intestine 36 days after initiating stem cell transformation (FIG. 21f ).

To further investigate the hierarchy that exists between the APC-deficient stem cells and their transformed progeny, we examined expression of the stem cell marker protein Lgr5-EGFP during the various stages of adenoma formation in our model. In non-transformed stem cells, Lgr5-EGFP expression was restricted to the Crypt Base Columnar (CBC) cells (FIG. 22a ). Expression of this stem cell marker was maintained following the initial transformation of the stem cells after 3 days (FIG. 22b ) and was also clearly evident in the “pockets” of recently expanded transformed progeny within the crypts after 8 days (FIG. 22c ), indicating that at least some aspect of “stemness” was conferred to these cells. However, there was a marked down-regulation of Lgr5-EGFP expression on the larger adenomas present in the intestines of 36-day induced mice, despite uniformly high ß-catenin levels throughout the tumor (FIG. 22d ). Lgr5-EGFP expression was limited to a few scattered cells within the tumor mass (FIG. 23). These GFP-positive cells retained the slender, wedge-shaped morphology characteristic of the CBC intestinal stem cells. It is therefore tempting to speculate that the Lgr5 expression in larger adenomas is marking a rare population of stem cells responsible for fueling their continued growth. Taken together, these data demonstrate that transformation of stem cells through loss of Apc is an extremely efficient route towards initiating intestinal adenoma formation. The kinetics of this process suggest that no further mutations are required once both Apc alleles are lost in intestinal epithelium, which is in accordance with the tissue-tropism of Apc's tumor suppressor activity.

Example 5 Generation and Use of Antibodies Directed Against LGR5 and LGR6 Materials and Methods

Monoclonal rat antibodies were generated by Genovac (Freiburg, Germany) by intramuscular injection of rats with an expression plasmid expressing either human Lgr5 or Lgr6. Rat B-cells were fused with mouse myeloma cells. The resulting hybridomas were screened on HEK293 cells that were transfected with human or Mouse Lgr5 or Lgr6 expression plasmids.

L8 (DNTcf4-LS174T) cells were cultured with and without Doxycycline for 48 hrs. L8 cells are clonal derivatives of LS174T cells. Upon Doxycycline (DOX) induction the L8 cells express a dominant negative form of T-cell Factor 4 (DNTcf4; see Roose et al., 1999, Science 285: 1923-1926). DNTcf4 turns off constitutive active Wnt pathway. Rat IgG was used as negative isotype control. After 48 hrs cells are washed with ice cold PBS and brought into suspension using 5 mM EDTA. All the following steps are done at 4° C. Cells were blocked for 30 min in PBS containing 2% BSA. Primary (1st) and Secondary (2nd) antibody reagent were incubated subsequently for 1 hr, and washed with ice cold PBS/2% BSA. For the primary antibody staining we used undiluted hybridoma supernatant, 2nd antibody staining was done using Qdot® 655 goat F(ab′)2 anti-rat IgG conjugates (H+L) (Molecular Probes/Invitrogen). Prior to analysis propidium iodine was added to exclude dead cells in the analysis.

Results

The specificity of some of the isolated antibodies is shown in Tables 4 and 5, as tested by FACS analysis. 9G5 is a rat monoclonal antibody directed against hLgr5. The analysis of endogenous Lgr5 expression was determined in L8 cells. L8 cells are clonal derivatives of LS174T cells. Upon Doxycycline (DOX) induction, L8 cells express dominant negative Tcf4 (DNTcf4). DNTcf4 turns off constitutive active Wnt pathway. This is reflected in FIG. 24, showing FACS staining of L8 cells with 9G5 antibody or IgG control antibody. After 48 hrs of DOX induction, indeed a reduction in endogenous hLgr5 protein levels was observed, as also becomes clear from the reduction in the fluorescent means of the peak for the L8 cells treated with doxycycline.

This experiment was also performed with LGR5-specific antibodies 2F10, 10C1 and 6C10. As shown in FIG. 26, similar results are obtained with any of these LGR5-specific antibodies.

TABLE 4 Specificity of Lgr5 antibodies. 9G5 recognize both mouse and human Lgr5. The colon cancer cell lines; DLD1 and SW480, LIM1863 do not show specific staining for Lgr5. These antibodies were tested negative for cross reactivity against mouse Lgr4, 6 and human Lgr4, and 6. L8 mLgr5-293T hLgr5-293T (DNTcf4- overexpression overexpression LS174 LS174) NR 1D9 − + + + NR 2F10 − + + + NR 4D11 − + + + NR 6C10 − + + + NR 9B3 − + + + NR 3A4 − + + + NR 5A7 − + + + NR 6G2 − + + + NR 9G5 ++ ++ ++ ++ NR 2B8 − ++ ++ ++ NR 3B9 − ++ ++ ++ NR 5C8 − + + + NR 7B11 − + + + NR10C1 − + + + NR 4D6 − + + + NR 5E9 − + + + NR 8F2 − ++ ++ ++ NR10F7 − + + +

TABLE 5 Specificity of Lgr6 antibodies. Antibodies 1d8 and 3d8 recognize mouse Lgr6 and hLgr5 in addition to human Lgr6. The colon cancer cell lines; LS174, DLD1 and SW480 do not show specific staining for Lgr6. These antibodies were tested negative for cross reactivity against mouse Lgr4, 5 and human Lgr4. Clone number 1d8 3d8 6d8 2f4 2h10 5e10 hLgr5-293T + + − − − − overexpression mLgr6-293T + + − − − − overexpression hLgr6-293T ++ ++ ++ ++ + ++ overexpression LS174 − − − − − − L8 (LS174- − − − − − − DNTcf4)

Example 6 Expression Analysis of Colon and Small Intestine Derived Stem Cells Compared to their Direct Progeny Materials and Methods Isolation of GFP Positive Epithelial Cells

Freshly isolated small intestines or colons were incised along their length and villi (in case of small intestine) were removed by scraping. The tissue was then incubated in PBS/5 mM EDTA for 5 minutes. Gentle shaking removed remaining villi and the intestinal tissue was subsequently incubated in PBS/EDTA for 30 minutes at 4° C. Vigorous shaking yielded free crypts which were incubated in PBS supplemented with Trypsine (10 mg/ml) and DNAse (0.8 u/μl) for 30 minutes at 37° C. After incubation, cells were spun down, resuspended in SMEM (Invitrogen) and filtered through a 40 μM mesh. GFP-expressing cells were isolated using a MoFlo cell sorter (DAKO).

Microarray Analysis

RNA was isolated from the GFP^(hi) and GFP^(lo) cell fractions of intestines from Lgr5-EGFP-ires-CreERT2 mice. 250 ng of total RNA was labeled using low RNA Input Linear Amp kit (Agilent Technologies, Pato Alto, Calif., USA). Labeling, hybridization, and washing protocols were done according to guidelines (Agilent Technologies, Santa Clara, Calif., USA). Differentially labelled cRNA from GFP^(hi) and GFP^(lo) cells from two different sorts (each combining three different mice) were combined and hybridised on 4×44K Agilent Whole Mouse Genome dual colour Microarrays (G4122F) in two dye swap experiments, resulting in four individual arrays. All data analyses were performed using ArrayAssist (Stratagene Inc, La Jolla, Calif., USA) and Microsoft Excel (Microsoft Corporation, Redmond, Wash., USA). Raw signal intensities were corrected by subtracting local background. Negative values were changed by a positive value close to zero (standard deviation of the local background) in order to allow calculation of rations between intensities for features only present in one sample (GFP^(hi) or GFP^(lo)). Data were filtered if both (GFP^(hi) or GFP^(lo)) intensities were changed or if both intensities were less than two time the background signal and normalized by a Loess algorithm. Statistical analysis was performed by running an Excel version of SAM (Significant Analysis of Microarrays) using an Excel plug-in of the software (Tusher PNAS 2001, References 6) and “one class” as the response value. Genes were considered to be significantly enriched in GFP^(hi) cells if they had a q-value of <0.1 and where present in at least 3 out of 4 arrays and the average of all four arrays exceeded a log 2 ration of 0.6.

Results

In order to define a gene expression profile for Lgr5⁺ intestinal stem cells, we established a protocol to sort GFP-positive epithelial cells from cell suspensions prepared from freshly isolated crypts of Lgr5-EGFP-ires-CreERT2 mice (see Methods). FACS analysis distinguished a GFP-high (GFP^(hi)) and a GFP-low (GFP^(lo)) population, which we tentatively identified as CBC cells and their immediate transit-amplifying daughters, respectively (FIG. 25). A single mouse intestine routinely yielded several hundred thousand GFP^(hi) and GFP^(lo) cells. An example of an almost pure population of Lgr5-expressing cells is provided in FIG. 25A. In order to identify novel stem cell genes, mRNA samples of the two populations were subjected to comparative gene expression profiling. The gene that was most highly enriched in the GFP^(hi) cells was, satisfactorily, the Lgr5 gene itself. Multiple genes on the list (Table 6) were already identified as intestinal Wnt target genes previously, for instance in human colon cancer (van der Flier et al, 2007, Gastroenterology 132, 628-632), which further validated the gene list. While in situ hybridizations on these Wnt target genes typically confirmed high level expression in CBC cells, TA cells directly above the Paneth cells also expressed these genes, albeit at a much lower level. As an example, FIG. 25B shows the expression of Sox9, a Wnt-responsive gene (Blache et al., 2004) crucial for Paneth cell specification (Bastide et al., 2007; Mori-Akiyama et al., 2007).

Discussion

In the intestine, a long-lived pool of cycling stem cells is defined by Lgr5 expression, a Wnt responsive orphan G-coupled receptor (Barker et al., 2007, Nature 449, 1003-1007). These Lgr5⁺ cells have previously been observed by Leblond and colleagues, who named them Crypt Base Columnar (CBC) cells and already speculated that these CBC cells represent the stem cells of the intestinal epithelium (Cheng and Leblond, 1974, Am J Anat 141, 461-79). Here, we define a minimal gene expression profile for these CBC cells by exploiting the Lgr5-EGFP-ires-CreERT2 knock-in mice for sorting, based on GFP expression. We defined a set genes differently expressed between GFP^(hi) and GFP^(lo) fractions. Based on confocal images of isolated crypts, we tentatively identified these as CBC cells and their daughters, respectively. Lgr5 was found as the most differential gene in this set, implying that its expression is strongly restricted to CBC cells. Many other genes in the signature represented previously identified Wnt-dependent genes, e.g. Ascl2, CD44, Ephb3, Sox9 and Sp5 (van der Flier et al, 2007, Gastroenterology 132, 628-632). Given the intimate connection between Wnt signaling and the biology of stem cells in many tissues (Reya and Clevers, 2005, Nature 434, 843-850), this was not surprising.

Table 6 Expression Analysis of Stem Cells and their Direct Progeny

Small intestinal (Table 6a) and colon stem cell (Table 6b) signature based on Lgr5 expression. GFP-positive epithelial cells from pure crypt preparations of Lgr5-EGFP-ires-CreERT2 mice were isolated using FACS sorting. FACS analysis distinguished two populations GFP^(hi) and GFP^(lo) cells, corresponding to the CBC cells and their immediate transit-amplifying daughters respectively. In order to identify novel stem cell genes, mRNA samples of the two populations were subjected to comparative gene expression profiling using Agilent microarray analysis.

TABLE 6a Comparison of small intestinal stem cells with direct progeny avg log2 ratio¹ Gene name (gfp^(high)/gfp^(low)) Lgr5 2.54 Ephb3 1.38 Cd44 1.15 Rnf43 1.14 Sox9 1.12 Slc12a2 0.87 Ets2 0.80 ¹Q value <0.15

TABLE 6b Comparison of colon stem cells with direct progeny avg log2 ratio¹ Gene name (gfp^(high)/gfp^(low)) Lgr5 2.98 Cd44 1.47 Cdca7 1.23 Ephb3 1.11 Myb 0.81 Myc 0.77 ¹Q value <0.05

Example 7 Sequence Determination of Light Chain and Heavy Chains, Including CDR Regions, of LGR5-Specific/LGR6-Specific Antibodies Materials and Methods: Hybridoma Sequence

The hybridomas were produced as described in the materials and methods section of Example 5.

Hybridoma sequences were determined from Lgr5-specific and/or Lgr6-specific clonal hybridoma cell lines NR 2F10 (see Table 4) and 6d8 and 2f4 (see Table 5). Total RNA was isolated using Trizol reagent and cDNA generated using superscript reverse transcriptase (Promega). cDNA was amplified using PCR primers designed to amplify the IgG antibody Fv-DNA sequences in a ‘touch-down’ PCR. PCR fragments were cloned into either PJET1.2 (Fermentas) or PGEM-T (Promega) cloning vectors and subsequently sequenced using vector-specific primers on an ABI sequencer.

IgG Antibody Fc-DNA Sequence PCR Primers: Kappa L-Chain Reverse Primers; 25 Individually Synthesized Oligos, Pooled, Representing 50 Variants:

MVK-1 GACATTGTTCTCACCCAGTCTCC MVK-2 GACATTGTGCTSACCCAGTCTCC MVK-3 GACATTGTGATGACTCAGTCTCC MVK-4 GACATTGTGCTMACTCAGTCTCC MVK-5 GACATTGTGYTRACACAGTCTCC MVK-6 GACATTGTRATGACACAGTCTCC MVK-7 GACATTMAGATRACCCAGTCTCC MVK-8 GACATTGCAGATGAMCCAGTCTCC MVK-9 GACATTCAGATGACDCAGTCTCC MVK-10 GACATTCAGATGACACAGACTAC MVK-11 GACATTCAGATGATTCAGTCTCC MVK-12 GACATTGTTCTCAWCCAGTCTCC MVK-13 GACATTGTTCTCTCCCAGTCTCC MVK-14 GACATTGWGCTSACCCAATCTCC MVK-15 GACATTSTGATGACCCARTCTC MVK-16 GACATTKTGATGACCCARACTCC MVK-17 GACATTGTGATGACTCAGGCTAC MVK-18 GACATTGTGATGACBCAGGCTGC MVK-19 GACATTGTGATAACYCAGGATG MVK-20 GACATTGTGATGACCCAGTTTGC MVK-21 GACATTGTGATGACACAACCTGC MVK-22 GACATTGTGATGACCCAGATTCC MVK-23 GACATTTTGCTGACTCAGTCTCC MVK-24 GACATTGTAATGACCCAATCTCC MVK-25 GACATTGTGATGACCCACACTCC

Kappa L-Chain Forward Primer:

mck-1 ACACTCATTCCTGTTGAAGCTCTTGAC

H-Chain Variable Region Reverse Primers, 25 Individually Synthesized Oligos, Pooled, Representing 88 Variants:

MVH-1 GCCGGCCATGGCCGAGGTRMAGCTTCAGGAGTCAGGAC MVH-2 GCCGGCCATGGCCGAGGTSCAGCTKCAGCAGTCAGGAC MVH-3 GCCGGCCATGGCCCAGGTGCAGCTGAAGSASTCAGG MVH-4 GCCGGCCATGGCCGAGGTGCAGCTTCAGGAGTCSGGAC MVH-5 GCCGGCCATGGCCGARGTCCAGCTGCAACAGTCYGGAC MVH-6 GCCGGCCATGGCCCAGGTCCAGCTKCAGCAATCTGG MVH-7 GCCGGCCATGGCCCAGSTBCAGCTGCAGCAATCTGG MVH-8 GCCGGCCATGGCCCAGGTYCAGCTGCAGCAGTCTGGRC MVH-9 GCCGGCCATGGCCCAGGTYCAGCTYCAGCAGTCTGG MVH-10 GCCGGCCATGGCCGAGGTCCARCTGCAACAATCTGGACC MVH-11 GCCGGCCATGGCCCAGGTCCACGTGAAGCAGTCTGGG MVH-12 GCCGGCCATGGCCGAGGTGAASSTGGTGGAATCTG MVH-13 GCCGGCCATGGCCGAVGTGAAGYTGGTGGAGTCTG MVH-14 GCCGGCCATGGCCGAGGTGCAGSKGGTGGAGTCTGGGG MVH-15 GCCGGCCATGGCCGAKGTGCAMCTGGTGGAGTCTGGG MVH-16 GCCGGCCATGGCCGAGGTGAAGCTGATGGARTCTGG MVH-17 GCCGGCCATGGCCGAGGTGCARCTTGTTGAGTCTGGTG MVH-18 GCCGGCCATGGCCGARGTRAAGCTTCTAGAGTCTGGA MVH-19 GCCGGCCATGGCCGAAGTGAARSTTGAGGAGTCTGG MVH-20 GCCGGCCATGGCCGAAGTGATGCTGGTGGAGTCTGGG MVH-21 GCCGGCCATGGCCCAGGTTACTCTRAAAGWGTSTGGCC MVH-22 GCCGGCCATGGCCCAGGTCCAACTVCAGCARCCTGG MVH-23 GCCGGCCATGGCCCAGGTYCARCTGCAGCAGTCTG MVH-24 GCCGGCCATGGCCGATGTGAACTTGGAAGTGTCTGG MVH-25 GCCGGCCATGGCCGAGGTGAAGGTCATCGAGTCTGG

H-Chain Forward Primers:

MJH-REV1&2 GGGGGTGTCGTTTTGGCTGAGGAGACGGTGACCGTGG MJH-REV2INT GGGGGTGTCGTTTTGGCTGAGGAGACGGTGACAGTGG MJH-REV3 GGGGGTGTCGTTTTGGCTGAGGAGACGGTGACCAGAG MJH-REV4 GGGGGTGTCGTTTTGGCTGAGGAGACGGTGACCGAGG

Variable Position Key: R (A/G); M (A/C); Y (T/C); W (A/T); S (G/C); K (G/T); H (A/T/C); B (G/C/T); V (G/A/C); D (G/A/T); N (G/A/T/C)

In this experiment, mouse-specific oligos are used. For more reproducible results, rat-specific oligos can be used as well.

Results

The light chain sequence of LGR5-specific antibody NR 2F10 (see Table 4) and the heavy chain sequences of LGR6-specific antibodies 6d8 and 2f4 (see Table 5) are depicted in FIG. 27. The CDR regions are indicated in bold and in italics. The CDR sequences were determined according to Kabat (Kabat et al., “Sequences of Proteins of Immunological Interest,” U.S. Dept. of Health and Human Services, National Institute of Health, 1987). Antibodies or functional equivalents thereof comprising at least one of these CDR sequences constitute a high affinity binding compound with a high specificity for their target proteins LGR5 and/or LGR6.

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1-19. (canceled)
 20. A method for testing the effect of a possible anti cancer stem cell compound comprising contacting a set of cancer stem cells in vitro with said possible anti cancer stem cell compound, wherein the set of cancer stem cells or cancer stem cells are a) cancer stem cells comprising Lgr6 and/or Lgr5 embedded in their cell membrane; and/or b) obtainable by a method comprising: optionally preparing a cell suspension from a solid or liquid tumor sample contacting said cell suspension with an Lgr6 and/or 5 binding compound identifying the cells bound to said binding compound optionally isolating the cancer stem cells from said binding compound, and testing whether said treated cancer stem cells are capable of generating a continuously growing tumor and wherein said possible cancer stem cell medicament is preferably designed as an Lgr5 or 6 inhibitor or as an Lgr5 or 6 binding compound. 21-56. (canceled)
 57. The method according to claim 20, further comprising contacting said possible anti cancer stem cell compound with a tissue or organ stem cell and selecting a compound that specifically effects tumour stem cells.
 58. (canceled)
 59. An in vitro method for identifying a compound that can be used in cancer treatment, comprising contacting an isolated collection of stem cells, wherein the stem cells comprise cancer stem cells comprising Lgr5 in their cell membranes, with a possible anti-cancer stem cell compound.
 60. A method for testing the anti-cancer stem cell efficacy of a compound comprising: a) contacting a collection of cancer stem cells with an anti-Lgr5 and/or Lgr6 binding compound a first time, wherein the collection of cancer stem cells comprises Lgr5 and/or Lgr6 in their cell membrane; b) contacting the collection of cancer stem cells with a compound; c) contacting the collection of cancer stem cells with an anti-Lgr5 and/or Lgr6 binding compound a second time; and d) determining the change in the number of cancer stem cells in the collection of cancer stem cells.
 61. The method of claim 60, wherein the collection of cancer stem cells comprises at least 50% Lgr5 and/or Lgr6 positive stem cells, at least 60% Lgr5 and/or Lgr6 positive stem cells, at least 70% Lgr5 and/or Lgr6 positive stem cells, at least 80% Lgr5 and/or Lgr6 positive stem cells, at least 90% Lgr5 and/or Lgr6 positive stem cells, or at least 95% Lgr5 and/or Lgr6 positive stem cells.
 62. The method of claim 61, wherein the cancer stem cells comprising Lgr5 and/or Lgr6 are capable of generating a continuously growing tumor.
 63. The method of claim 60, wherein the compound is an Lgr5 and/or Lgr6 inhibitor.
 64. The method of claim 63, wherein the compound is a small molecule that interferes with the biological activity of Lgr5 and/or Lgr6.
 65. The method of claim 63 wherein the Lgr5 and/or Lgr6 binding compound is an antibody, an antibody derivative, or an antibody fragment capable of binding to Lgr5 and/or Lgr6.
 66. The method of claim 60, wherein the method further comprises identifying a compound that specifically targets cancer stem cells comprising Lgr5 and/or Lgr6 in their cell membrane.
 67. The method of claim 60, wherein the cancer stem cells comprising Lgr5 and/or Lgr6 in their cell membrane are recombinant.
 68. The method of claim 60, wherein the method is a high-throughput method.
 69. The method of claim 60, wherein the method further comprises e) quantifying the number of non-cancerous epithelial stem cells in the collection of cancer stem cells; f) contacting the non-cancerous epithelial stem cells with a compound; g) quantifying the number of non-cancerous epithelial stem cells in the collection of cancer stem cells a second time; and h) determining the change in the number of non-cancerous epithelial stem cells in the collection of cancer stem cells thereby identifying a compound that specifically targets cancer stem cells comprising Lgr5 and/or Lgr6 in their cell membrane. 